diff --git a/docs/app/experiments/slider-marks.tsx b/docs/app/experiments/slider-marks.tsx
index 3aca9f132..81cf3f6cd 100644
--- a/docs/app/experiments/slider-marks.tsx
+++ b/docs/app/experiments/slider-marks.tsx
@@ -1,7 +1,7 @@
 'use client';
 import * as React from 'react';
 import { Slider } from '@base_ui/react/Slider';
-import { useSliderContext } from '../../../packages/mui-base/src/Slider/Root/SliderContext';
+import { useSliderRootContext } from '../../../packages/mui-base/src/Slider/Root/SliderRootContext';
 
 const STOPS = [
   {
@@ -33,7 +33,7 @@ function getSliderThumbAriaValueText(value: number) {
 // for "inverted track", the track/rail can be styled with CSS but a prop is needed to flip the "mark active" state
 function MarkWithLabel(props: { index: number; value: number; label: string; inverted?: boolean }) {
   const { index, value, label, inverted = false } = props;
-  const { direction, values } = useSliderContext();
+  const { direction, values } = useSliderRootContext();
   const isRtl = direction === 'rtl';
   const isFilled = inverted ? value >= values[0] : values[0] >= value;
   return (
diff --git a/docs/app/experiments/slider-tooltip.tsx b/docs/app/experiments/slider-tooltip.tsx
index 28d89d685..690be39d7 100644
--- a/docs/app/experiments/slider-tooltip.tsx
+++ b/docs/app/experiments/slider-tooltip.tsx
@@ -3,7 +3,7 @@ import * as React from 'react';
 import { useTheme } from '@mui/system';
 import { Slider } from '@base_ui/react/Slider';
 import { Tooltip } from '@base_ui/react/Tooltip';
-import { useSliderContext } from '../../../packages/mui-base/src/Slider/Root/SliderContext';
+import { useSliderRootContext } from '../../../packages/mui-base/src/Slider/Root/SliderRootContext';
 
 function useIsDarkMode() {
   const theme = useTheme();
@@ -74,7 +74,7 @@ export default function App() {
 
 const SliderMark = React.forwardRef(function SliderMark(props: any, ref: React.ForwardedRef<any>) {
   const { index, style, ...otherProps } = props;
-  const { percentageValues } = useSliderContext();
+  const { percentageValues } = useSliderRootContext();
   const isFilled = percentageValues[0] >= index * 10;
   return (
     <span
diff --git a/packages/mui-base/src/AlertDialog/Root/AlertDialogRootContext.ts b/packages/mui-base/src/AlertDialog/Root/AlertDialogRootContext.ts
index 2afa9dac6..f58c9a47c 100644
--- a/packages/mui-base/src/AlertDialog/Root/AlertDialogRootContext.ts
+++ b/packages/mui-base/src/AlertDialog/Root/AlertDialogRootContext.ts
@@ -18,10 +18,17 @@ export const AlertDialogRootContext = React.createContext<AlertDialogRootContext
   undefined,
 );
 
+if (process.env.NODE_ENV !== 'production') {
+  AlertDialogRootContext.displayName = 'AlertDialogRootContext';
+}
+
 export function useAlertDialogRootContext() {
   const context = React.useContext(AlertDialogRootContext);
   if (context === undefined) {
-    throw new Error('useAlertDialogRootContext must be used within an AlertDialogRoot');
+    throw new Error(
+      'Base UI: AlertDialogRootContext is missing. AlertDialog parts must be placed within <AlertDialog.Root>.',
+    );
   }
+
   return context;
 }
diff --git a/packages/mui-base/src/Checkbox/Root/CheckboxRootContext.ts b/packages/mui-base/src/Checkbox/Root/CheckboxRootContext.ts
index 580c1816a..88bb016f5 100644
--- a/packages/mui-base/src/Checkbox/Root/CheckboxRootContext.ts
+++ b/packages/mui-base/src/Checkbox/Root/CheckboxRootContext.ts
@@ -4,14 +4,19 @@ import type { CheckboxRoot } from './CheckboxRoot';
 
 export type CheckboxRootContext = CheckboxRoot.OwnerState;
 
-export const CheckboxRootContext = React.createContext<CheckboxRootContext | null>(null);
+export const CheckboxRootContext = React.createContext<CheckboxRootContext | undefined>(undefined);
+
+if (process.env.NODE_ENV !== 'production') {
+  CheckboxRootContext.displayName = 'CheckboxRootContext';
+}
 
 export function useCheckboxRootContext() {
   const context = React.useContext(CheckboxRootContext);
-  if (context === null) {
+  if (context === undefined) {
     throw new Error(
-      'Base UI: Checkbox.Indicator must be placed inside the Checkbox.Root component.',
+      'Base UI: CheckboxRootContext is missing. Checkbox parts must be placed within <Checkbox.Root>.',
     );
   }
+
   return context;
 }
diff --git a/packages/mui-base/src/CheckboxGroup/Root/CheckboxGroupRootContext.ts b/packages/mui-base/src/CheckboxGroup/Root/CheckboxGroupRootContext.ts
index 0c4b461c5..7e9295ace 100644
--- a/packages/mui-base/src/CheckboxGroup/Root/CheckboxGroupRootContext.ts
+++ b/packages/mui-base/src/CheckboxGroup/Root/CheckboxGroupRootContext.ts
@@ -9,12 +9,21 @@ export interface CheckboxGroupRootContext {
   parent: UseCheckboxGroupParent.ReturnValue;
 }
 
-export const CheckboxGroupRootContext = React.createContext<CheckboxGroupRootContext | null>(null);
+export const CheckboxGroupRootContext = React.createContext<CheckboxGroupRootContext | undefined>(
+  undefined,
+);
+
+if (process.env.NODE_ENV !== 'production') {
+  CheckboxGroupRootContext.displayName = 'CheckboxGroupRootContext';
+}
 
 export function useCheckboxGroupRootContext(optional = true) {
   const context = React.useContext(CheckboxGroupRootContext);
-  if (context === null && !optional) {
-    throw new Error('Base UI: CheckboxGroupRootContext is not defined.');
+  if (context === undefined && !optional) {
+    throw new Error(
+      'Base UI: CheckboxGroupRootContext is missing. CheckboxGroup parts must be placed within <CheckboxGroup.Root>.',
+    );
   }
+
   return context;
 }
diff --git a/packages/mui-base/src/Collapsible/Panel/CollapsiblePanel.test.tsx b/packages/mui-base/src/Collapsible/Panel/CollapsiblePanel.test.tsx
index 9302b381f..0bea82d66 100644
--- a/packages/mui-base/src/Collapsible/Panel/CollapsiblePanel.test.tsx
+++ b/packages/mui-base/src/Collapsible/Panel/CollapsiblePanel.test.tsx
@@ -1,8 +1,8 @@
 import * as React from 'react';
 import { createRenderer } from '@mui/internal-test-utils';
 import { Collapsible } from '@base_ui/react/Collapsible';
-import { CollapsibleRootContext } from '../Root/CollapsibleRootContext';
 import { describeConformance } from '../../../test/describeConformance';
+import { CollapsibleRootContext } from '../Root/CollapsibleRootContext';
 
 const contextValue: CollapsibleRootContext = {
   animated: false,
diff --git a/packages/mui-base/src/Collapsible/Root/CollapsibleRootContext.ts b/packages/mui-base/src/Collapsible/Root/CollapsibleRootContext.ts
index 98a7491ad..d19cffcb7 100644
--- a/packages/mui-base/src/Collapsible/Root/CollapsibleRootContext.ts
+++ b/packages/mui-base/src/Collapsible/Root/CollapsibleRootContext.ts
@@ -6,9 +6,7 @@ import type { CollapsibleRoot } from './CollapsibleRoot';
 export interface CollapsibleRootContext extends useCollapsibleRoot.ReturnValue {
   ownerState: CollapsibleRoot.OwnerState;
 }
-/**
- * @ignore - internal component.
- */
+
 export const CollapsibleRootContext = React.createContext<CollapsibleRootContext | undefined>(
   undefined,
 );
@@ -20,7 +18,10 @@ if (process.env.NODE_ENV !== 'production') {
 export function useCollapsibleRootContext() {
   const context = React.useContext(CollapsibleRootContext);
   if (context === undefined) {
-    throw new Error('useCollapsibleRootContext must be used inside a Collapsible component');
+    throw new Error(
+      'Base UI: CollapsibleRootContext is missing. Collapsible parts must be placed within <Collapsible.Root>.',
+    );
   }
+
   return context;
 }
diff --git a/packages/mui-base/src/Collapsible/Trigger/CollapsibleTrigger.test.tsx b/packages/mui-base/src/Collapsible/Trigger/CollapsibleTrigger.test.tsx
index 8f9ed3e74..289fc2969 100644
--- a/packages/mui-base/src/Collapsible/Trigger/CollapsibleTrigger.test.tsx
+++ b/packages/mui-base/src/Collapsible/Trigger/CollapsibleTrigger.test.tsx
@@ -1,8 +1,8 @@
 import * as React from 'react';
 import { createRenderer } from '@mui/internal-test-utils';
 import { Collapsible } from '@base_ui/react/Collapsible';
-import { CollapsibleRootContext } from '../Root/CollapsibleRootContext';
 import { describeConformance } from '../../../test/describeConformance';
+import { CollapsibleRootContext } from '../Root/CollapsibleRootContext';
 
 const contextValue: CollapsibleRootContext = {
   animated: false,
diff --git a/packages/mui-base/src/Composite/List/CompositeListContext.ts b/packages/mui-base/src/Composite/List/CompositeListContext.ts
index 07588d903..4f1358525 100644
--- a/packages/mui-base/src/Composite/List/CompositeListContext.ts
+++ b/packages/mui-base/src/Composite/List/CompositeListContext.ts
@@ -16,6 +16,10 @@ export const CompositeListContext = React.createContext<CompositeListContextValu
   elementsRef: { current: [] },
 });
 
+if (process.env.NODE_ENV !== 'production') {
+  CompositeListContext.displayName = 'CompositeListContext';
+}
+
 export function useCompositeListContext() {
   return React.useContext(CompositeListContext);
 }
diff --git a/packages/mui-base/src/Composite/Root/CompositeRoot.tsx b/packages/mui-base/src/Composite/Root/CompositeRoot.tsx
index 9876177ee..089addb88 100644
--- a/packages/mui-base/src/Composite/Root/CompositeRoot.tsx
+++ b/packages/mui-base/src/Composite/Root/CompositeRoot.tsx
@@ -39,7 +39,7 @@ const CompositeRoot = React.forwardRef(function CompositeRoot(
     extraProps: otherProps,
   });
 
-  const contextValue: CompositeRootContext.Value = React.useMemo(
+  const contextValue: CompositeRootContext = React.useMemo(
     () => ({ activeIndex, onActiveIndexChange }),
     [activeIndex, onActiveIndexChange],
   );
diff --git a/packages/mui-base/src/Composite/Root/CompositeRootContext.ts b/packages/mui-base/src/Composite/Root/CompositeRootContext.ts
index 69648f910..f92f119c9 100644
--- a/packages/mui-base/src/Composite/Root/CompositeRootContext.ts
+++ b/packages/mui-base/src/Composite/Root/CompositeRootContext.ts
@@ -1,19 +1,26 @@
 'use client';
 import * as React from 'react';
 
-export const CompositeRootContext = React.createContext<CompositeRootContext.Value | null>(null);
+export interface CompositeRootContext {
+  activeIndex: number;
+  onActiveIndexChange: (index: number) => void;
+}
+
+export const CompositeRootContext = React.createContext<CompositeRootContext | undefined>(
+  undefined,
+);
+
+if (process.env.NODE_ENV !== 'production') {
+  CompositeRootContext.displayName = 'CompositeRootContext';
+}
 
 export function useCompositeRootContext() {
   const context = React.useContext(CompositeRootContext);
-  if (context === null) {
-    throw new Error('<Composite.Item> must be used within <Composite.Root>');
+  if (context === undefined) {
+    throw new Error(
+      'Base UI: CompositeRootContext is missing. Composite parts must be placed within <Composite.Root>.',
+    );
   }
-  return context;
-}
 
-export namespace CompositeRootContext {
-  export interface Value {
-    activeIndex: number;
-    onActiveIndexChange: (index: number) => void;
-  }
+  return context;
 }
diff --git a/packages/mui-base/src/Dialog/Root/DialogRootContext.ts b/packages/mui-base/src/Dialog/Root/DialogRootContext.ts
index ade4da0cd..4514bc492 100644
--- a/packages/mui-base/src/Dialog/Root/DialogRootContext.ts
+++ b/packages/mui-base/src/Dialog/Root/DialogRootContext.ts
@@ -24,7 +24,10 @@ export const DialogRootContext = React.createContext<DialogRootContext | undefin
 export function useDialogRootContext() {
   const context = React.useContext(DialogRootContext);
   if (context === undefined) {
-    throw new Error('useDialogRootContext must be used within a DialogRoot');
+    throw new Error(
+      'Base UI: DialogRootContext is missing. Dialog parts must be placed within <Dialog.Root>.',
+    );
   }
+
   return context;
 }
diff --git a/packages/mui-base/src/Field/Root/FieldRootContext.ts b/packages/mui-base/src/Field/Root/FieldRootContext.ts
index d7966e262..9ea94220b 100644
--- a/packages/mui-base/src/Field/Root/FieldRootContext.ts
+++ b/packages/mui-base/src/Field/Root/FieldRootContext.ts
@@ -70,7 +70,9 @@ export function useFieldRootContext(optional = true) {
   const context = React.useContext(FieldRootContext);
 
   if (context.setControlId === NOOP && !optional) {
-    throw new Error('Base UI: Field components must be placed within <Field.Root>.');
+    throw new Error(
+      'Base UI: FieldRootContext is missing. Field parts must be placed within <Field.Root>.',
+    );
   }
 
   return context;
diff --git a/packages/mui-base/src/Form/Root/FormRootContext.ts b/packages/mui-base/src/Form/Root/FormRootContext.ts
index 8eb9bf6da..35370255d 100644
--- a/packages/mui-base/src/Form/Root/FormRootContext.ts
+++ b/packages/mui-base/src/Form/Root/FormRootContext.ts
@@ -28,6 +28,10 @@ export const FormRootContext = React.createContext<FormRootContext>({
   onClearErrors: () => {},
 });
 
+if (process.env.NODE_ENV !== 'production') {
+  FormRootContext.displayName = 'FormRootContext';
+}
+
 export function useFormRootContext() {
   return React.useContext(FormRootContext);
 }
diff --git a/packages/mui-base/src/Menu/CheckboxItem/MenuCheckboxItem.test.tsx b/packages/mui-base/src/Menu/CheckboxItem/MenuCheckboxItem.test.tsx
index c962d100d..9bfeb83b5 100644
--- a/packages/mui-base/src/Menu/CheckboxItem/MenuCheckboxItem.test.tsx
+++ b/packages/mui-base/src/Menu/CheckboxItem/MenuCheckboxItem.test.tsx
@@ -13,7 +13,7 @@ const testRootContext: MenuRootContext = {
   getPositionerProps: (p) => ({ ...p }),
   getTriggerProps: (p) => ({ ...p }),
   getItemProps: (p) => ({ ...p }),
-  parentContext: null,
+  parentContext: undefined,
   nested: false,
   triggerElement: null,
   setTriggerElement: () => {},
diff --git a/packages/mui-base/src/Menu/CheckboxItem/MenuCheckboxItemContext.ts b/packages/mui-base/src/Menu/CheckboxItem/MenuCheckboxItemContext.ts
index beab8db3f..9d2f631fe 100644
--- a/packages/mui-base/src/Menu/CheckboxItem/MenuCheckboxItemContext.ts
+++ b/packages/mui-base/src/Menu/CheckboxItem/MenuCheckboxItemContext.ts
@@ -13,7 +13,9 @@ export const MenuCheckboxItemContext = React.createContext<MenuCheckboxItemConte
 export function useMenuCheckboxItemContext() {
   const context = React.useContext(MenuCheckboxItemContext);
   if (context === undefined) {
-    throw new Error('useMenuCheckboxItemContext must be used within a MenuCheckboxItemProvider');
+    throw new Error(
+      'Base UI: MenuCheckboxItemContext is missing. MenuCheckboxItem parts must be placed within <Menu.CheckboxItem>.',
+    );
   }
 
   return context;
diff --git a/packages/mui-base/src/Menu/Group/MenuGroupContext.ts b/packages/mui-base/src/Menu/Group/MenuGroupContext.ts
index b3c97d8a9..b4e46d8cc 100644
--- a/packages/mui-base/src/Menu/Group/MenuGroupContext.ts
+++ b/packages/mui-base/src/Menu/Group/MenuGroupContext.ts
@@ -12,7 +12,7 @@ if (process.env.NODE_ENV !== 'production') {
 
 export function useMenuGroupRootContext() {
   const context = React.useContext(MenuGroupContext);
-  if (context == null) {
+  if (context === undefined) {
     throw new Error('Base UI: Missing MenuGroupRootContext provider');
   }
 
diff --git a/packages/mui-base/src/Menu/Item/MenuItem.test.tsx b/packages/mui-base/src/Menu/Item/MenuItem.test.tsx
index 1195d4f17..918d08d8f 100644
--- a/packages/mui-base/src/Menu/Item/MenuItem.test.tsx
+++ b/packages/mui-base/src/Menu/Item/MenuItem.test.tsx
@@ -13,7 +13,7 @@ const testRootContext: MenuRootContext = {
   getPositionerProps: (p) => ({ ...p }),
   getTriggerProps: (p) => ({ ...p }),
   getItemProps: (p) => ({ ...p }),
-  parentContext: null,
+  parentContext: undefined,
   nested: false,
   triggerElement: null,
   setTriggerElement: () => {},
diff --git a/packages/mui-base/src/Menu/Popup/MenuPopup.test.tsx b/packages/mui-base/src/Menu/Popup/MenuPopup.test.tsx
index cf5904881..6c6542b65 100644
--- a/packages/mui-base/src/Menu/Popup/MenuPopup.test.tsx
+++ b/packages/mui-base/src/Menu/Popup/MenuPopup.test.tsx
@@ -10,7 +10,7 @@ const testRootContext: MenuRootContext = {
   getPositionerProps: (p) => ({ ...p }),
   getTriggerProps: (p) => ({ ...p }),
   getItemProps: (p) => ({ ...p }),
-  parentContext: null,
+  parentContext: undefined,
   nested: false,
   triggerElement: null,
   setTriggerElement: () => {},
diff --git a/packages/mui-base/src/Menu/Positioner/MenuPositioner.test.tsx b/packages/mui-base/src/Menu/Positioner/MenuPositioner.test.tsx
index 70adbf142..2a89d5f0c 100644
--- a/packages/mui-base/src/Menu/Positioner/MenuPositioner.test.tsx
+++ b/packages/mui-base/src/Menu/Positioner/MenuPositioner.test.tsx
@@ -12,7 +12,7 @@ const testRootContext: MenuRootContext = {
   getPositionerProps: (p) => ({ ...p }),
   getTriggerProps: (p) => ({ ...p }),
   getItemProps: (p) => ({ ...p }),
-  parentContext: null,
+  parentContext: undefined,
   nested: false,
   triggerElement: null,
   setTriggerElement: () => {},
diff --git a/packages/mui-base/src/Menu/Positioner/MenuPositionerContext.ts b/packages/mui-base/src/Menu/Positioner/MenuPositionerContext.ts
index 8e3ad8a1c..fa72df76e 100644
--- a/packages/mui-base/src/Menu/Positioner/MenuPositionerContext.ts
+++ b/packages/mui-base/src/Menu/Positioner/MenuPositionerContext.ts
@@ -16,7 +16,9 @@ export interface MenuPositionerContext {
   arrowStyles: React.CSSProperties;
 }
 
-export const MenuPositionerContext = React.createContext<MenuPositionerContext | null>(null);
+export const MenuPositionerContext = React.createContext<MenuPositionerContext | undefined>(
+  undefined,
+);
 
 if (process.env.NODE_ENV !== 'production') {
   MenuPositionerContext.displayName = 'MenuPositionerContext';
@@ -24,8 +26,10 @@ if (process.env.NODE_ENV !== 'production') {
 
 export function useMenuPositionerContext() {
   const context = React.useContext(MenuPositionerContext);
-  if (context === null) {
-    throw new Error('<Menu.Popup> must be used within the <Menu.Positioner> component');
+  if (context === undefined) {
+    throw new Error(
+      'Base UI: MenuPositionerContext is missing. MenuPositioner parts must be placed within <Menu.Positioner>.',
+    );
   }
   return context;
 }
diff --git a/packages/mui-base/src/Menu/RadioGroup/MenuRadioGroupContext.ts b/packages/mui-base/src/Menu/RadioGroup/MenuRadioGroupContext.ts
index 10ac8dc81..1b8332f8b 100644
--- a/packages/mui-base/src/Menu/RadioGroup/MenuRadioGroupContext.ts
+++ b/packages/mui-base/src/Menu/RadioGroup/MenuRadioGroupContext.ts
@@ -5,7 +5,9 @@ export interface MenuRadioGroupContext {
   setValue: (newValue: any, event: Event) => void;
 }
 
-export const MenuRadioGroupContext = React.createContext<MenuRadioGroupContext | null>(null);
+export const MenuRadioGroupContext = React.createContext<MenuRadioGroupContext | undefined>(
+  undefined,
+);
 
 if (process.env.NODE_ENV !== 'production') {
   MenuRadioGroupContext.displayName = 'MenuRadioGroupContext';
@@ -13,8 +15,10 @@ if (process.env.NODE_ENV !== 'production') {
 
 export function useMenuRadioGroupContext() {
   const context = React.useContext(MenuRadioGroupContext);
-  if (context === null) {
-    throw new Error('useMenuRadioGroupContext must be used within a MenuRadioGroup');
+  if (context === undefined) {
+    throw new Error(
+      'Base UI: MenuRadioGroupContext is missing. MenuRadioGroup parts must be placed within <Menu.RadioGroup>.',
+    );
   }
 
   return context;
diff --git a/packages/mui-base/src/Menu/RadioItem/MenuRadioItem.test.tsx b/packages/mui-base/src/Menu/RadioItem/MenuRadioItem.test.tsx
index ba44c1972..00f68560c 100644
--- a/packages/mui-base/src/Menu/RadioItem/MenuRadioItem.test.tsx
+++ b/packages/mui-base/src/Menu/RadioItem/MenuRadioItem.test.tsx
@@ -14,7 +14,7 @@ const testRootContext: MenuRootContext = {
   getPositionerProps: (p) => ({ ...p }),
   getTriggerProps: (p) => ({ ...p }),
   getItemProps: (p) => ({ ...p }),
-  parentContext: null,
+  parentContext: undefined,
   nested: false,
   triggerElement: null,
   setTriggerElement: () => {},
diff --git a/packages/mui-base/src/Menu/RadioItem/MenuRadioItemContext.ts b/packages/mui-base/src/Menu/RadioItem/MenuRadioItemContext.ts
index 760b3618d..f40dc4894 100644
--- a/packages/mui-base/src/Menu/RadioItem/MenuRadioItemContext.ts
+++ b/packages/mui-base/src/Menu/RadioItem/MenuRadioItemContext.ts
@@ -10,10 +10,16 @@ export const MenuRadioItemContext = React.createContext<MenuRadioItemContext | u
   undefined,
 );
 
+if (process.env.NODE_ENV !== 'production') {
+  MenuRadioItemContext.displayName = 'MenuRadioItemContext';
+}
+
 export function useMenuRadioItemContext() {
   const context = React.useContext(MenuRadioItemContext);
   if (context === undefined) {
-    throw new Error('useMenuRadioItemContext must be used within a MenuRadioItemProvider');
+    throw new Error(
+      'Base UI: MenuRadioItemContext is missing. MenuRadioItem parts must be placed within <Menu.RadioItem>.',
+    );
   }
 
   return context;
diff --git a/packages/mui-base/src/Menu/Root/MenuRootContext.ts b/packages/mui-base/src/Menu/Root/MenuRootContext.ts
index a834e3da4..d00e0f939 100644
--- a/packages/mui-base/src/Menu/Root/MenuRootContext.ts
+++ b/packages/mui-base/src/Menu/Root/MenuRootContext.ts
@@ -6,23 +6,25 @@ export interface MenuRootContext extends useMenuRoot.ReturnValue {
   clickAndDragEnabled: boolean;
   disabled: boolean;
   nested: boolean;
-  parentContext: MenuRootContext | null;
+  parentContext: MenuRootContext | undefined;
   setClickAndDragEnabled: React.Dispatch<React.SetStateAction<boolean>>;
   typingRef: React.RefObject<boolean>;
 }
 
-export const MenuRootContext = React.createContext<MenuRootContext | null>(null);
+export const MenuRootContext = React.createContext<MenuRootContext | undefined>(undefined);
 
 if (process.env.NODE_ENV !== 'production') {
   MenuRootContext.displayName = 'MenuRootContext';
 }
 
 function useMenuRootContext(optional?: false): MenuRootContext;
-function useMenuRootContext(optional: true): MenuRootContext | null;
+function useMenuRootContext(optional: true): MenuRootContext | undefined;
 function useMenuRootContext(optional?: boolean) {
   const context = React.useContext(MenuRootContext);
-  if (context === null && !optional) {
-    throw new Error('Base UI: MenuRootContext is not defined.');
+  if (context === undefined && !optional) {
+    throw new Error(
+      'Base UI: MenuRootContext is missing. Menu parts must be placed within <Menu.Root>.',
+    );
   }
 
   return context;
diff --git a/packages/mui-base/src/Menu/SubmenuTrigger/SubmenuTrigger.tsx b/packages/mui-base/src/Menu/SubmenuTrigger/SubmenuTrigger.tsx
index 4a32fdfde..9161e512f 100644
--- a/packages/mui-base/src/Menu/SubmenuTrigger/SubmenuTrigger.tsx
+++ b/packages/mui-base/src/Menu/SubmenuTrigger/SubmenuTrigger.tsx
@@ -36,7 +36,7 @@ const SubmenuTrigger = React.forwardRef(function SubmenuTriggerComponent(
     typingRef,
   } = useMenuRootContext();
 
-  if (parentContext === null) {
+  if (parentContext === undefined) {
     throw new Error('Base UI: ItemTrigger must be placed in a nested Menu.');
   }
 
diff --git a/packages/mui-base/src/Menu/Trigger/MenuTrigger.test.tsx b/packages/mui-base/src/Menu/Trigger/MenuTrigger.test.tsx
index 305d9ad81..48e67d7a0 100644
--- a/packages/mui-base/src/Menu/Trigger/MenuTrigger.test.tsx
+++ b/packages/mui-base/src/Menu/Trigger/MenuTrigger.test.tsx
@@ -12,7 +12,7 @@ const testRootContext: MenuRootContext = {
   getPositionerProps: (p) => ({ ...p }),
   getTriggerProps: (p) => ({ ...p }),
   getItemProps: (p) => ({ ...p }),
-  parentContext: null,
+  parentContext: undefined,
   nested: false,
   triggerElement: null,
   setTriggerElement: () => {},
diff --git a/packages/mui-base/src/NumberField/Decrement/NumberFieldDecrement.test.tsx b/packages/mui-base/src/NumberField/Decrement/NumberFieldDecrement.test.tsx
index 2ca25b155..ad0800657 100644
--- a/packages/mui-base/src/NumberField/Decrement/NumberFieldDecrement.test.tsx
+++ b/packages/mui-base/src/NumberField/Decrement/NumberFieldDecrement.test.tsx
@@ -4,7 +4,7 @@ import { screen, fireEvent } from '@mui/internal-test-utils';
 import { NumberField } from '@base_ui/react/NumberField';
 import { createRenderer, describeConformance } from '#test-utils';
 import { CHANGE_VALUE_TICK_DELAY, START_AUTO_CHANGE_DELAY } from '../utils/constants';
-import { NumberFieldContext } from '../Root/NumberFieldContext';
+import { NumberFieldRootContext } from '../Root/NumberFieldRootContext';
 
 const testContext = {
   getDecrementButtonProps: (externalProps) => externalProps,
@@ -15,7 +15,7 @@ const testContext = {
     invalid: false,
     readOnly: false,
   },
-} as NumberFieldContext;
+} as NumberFieldRootContext;
 
 describe('<NumberField.Decrement />', () => {
   const { render, clock } = createRenderer();
@@ -24,7 +24,9 @@ describe('<NumberField.Decrement />', () => {
     refInstanceof: window.HTMLButtonElement,
     render(node) {
       return render(
-        <NumberFieldContext.Provider value={testContext}>{node}</NumberFieldContext.Provider>,
+        <NumberFieldRootContext.Provider value={testContext}>
+          {node}
+        </NumberFieldRootContext.Provider>,
       );
     },
   }));
diff --git a/packages/mui-base/src/NumberField/Decrement/NumberFieldDecrement.tsx b/packages/mui-base/src/NumberField/Decrement/NumberFieldDecrement.tsx
index 4d9c71cf1..049500f80 100644
--- a/packages/mui-base/src/NumberField/Decrement/NumberFieldDecrement.tsx
+++ b/packages/mui-base/src/NumberField/Decrement/NumberFieldDecrement.tsx
@@ -1,7 +1,7 @@
 'use client';
 import * as React from 'react';
 import PropTypes from 'prop-types';
-import { useNumberFieldContext } from '../Root/NumberFieldContext';
+import { useNumberFieldRootContext } from '../Root/NumberFieldRootContext';
 import { useComponentRenderer } from '../../utils/useComponentRenderer';
 import type { NumberFieldRoot } from '../Root/NumberFieldRoot';
 import { BaseUIComponentProps } from '../../utils/types';
@@ -23,7 +23,7 @@ const NumberFieldDecrement = React.forwardRef(function NumberFieldDecrement(
 ) {
   const { render, className, ...otherProps } = props;
 
-  const { getDecrementButtonProps, ownerState } = useNumberFieldContext('Decrement');
+  const { getDecrementButtonProps, ownerState } = useNumberFieldRootContext();
 
   const { renderElement } = useComponentRenderer({
     propGetter: getDecrementButtonProps,
diff --git a/packages/mui-base/src/NumberField/Group/NumberFieldGroup.test.tsx b/packages/mui-base/src/NumberField/Group/NumberFieldGroup.test.tsx
index bda5d52f1..167d3c78b 100644
--- a/packages/mui-base/src/NumberField/Group/NumberFieldGroup.test.tsx
+++ b/packages/mui-base/src/NumberField/Group/NumberFieldGroup.test.tsx
@@ -3,7 +3,7 @@ import { expect } from 'chai';
 import { screen } from '@mui/internal-test-utils';
 import { NumberField } from '@base_ui/react/NumberField';
 import { createRenderer, describeConformance } from '#test-utils';
-import { NumberFieldContext } from '../Root/NumberFieldContext';
+import { NumberFieldRootContext } from '../Root/NumberFieldRootContext';
 
 const testContext = {
   getGroupProps: (externalProps) => ({ role: 'group', ...externalProps }),
@@ -14,7 +14,7 @@ const testContext = {
     invalid: false,
     readOnly: false,
   },
-} as NumberFieldContext;
+} as NumberFieldRootContext;
 
 describe('<NumberField.Group />', () => {
   const { render } = createRenderer();
@@ -23,7 +23,9 @@ describe('<NumberField.Group />', () => {
     refInstanceof: window.HTMLDivElement,
     render(node) {
       return render(
-        <NumberFieldContext.Provider value={testContext}>{node}</NumberFieldContext.Provider>,
+        <NumberFieldRootContext.Provider value={testContext}>
+          {node}
+        </NumberFieldRootContext.Provider>,
       );
     },
   }));
diff --git a/packages/mui-base/src/NumberField/Group/NumberFieldGroup.tsx b/packages/mui-base/src/NumberField/Group/NumberFieldGroup.tsx
index e35913dd9..28d0f2589 100644
--- a/packages/mui-base/src/NumberField/Group/NumberFieldGroup.tsx
+++ b/packages/mui-base/src/NumberField/Group/NumberFieldGroup.tsx
@@ -1,7 +1,7 @@
 'use client';
 import * as React from 'react';
 import PropTypes from 'prop-types';
-import { useNumberFieldContext } from '../Root/NumberFieldContext';
+import { useNumberFieldRootContext } from '../Root/NumberFieldRootContext';
 import { useComponentRenderer } from '../../utils/useComponentRenderer';
 import type { NumberFieldRoot } from '../Root/NumberFieldRoot';
 import type { BaseUIComponentProps } from '../../utils/types';
@@ -23,7 +23,7 @@ const NumberFieldGroup = React.forwardRef(function NumberFieldGroup(
 ) {
   const { render, className, ...otherProps } = props;
 
-  const { getGroupProps, ownerState } = useNumberFieldContext('Group');
+  const { getGroupProps, ownerState } = useNumberFieldRootContext();
 
   const { renderElement } = useComponentRenderer({
     propGetter: getGroupProps,
diff --git a/packages/mui-base/src/NumberField/Increment/NumberFieldIncrement.test.tsx b/packages/mui-base/src/NumberField/Increment/NumberFieldIncrement.test.tsx
index dc90a6857..5b18c6963 100644
--- a/packages/mui-base/src/NumberField/Increment/NumberFieldIncrement.test.tsx
+++ b/packages/mui-base/src/NumberField/Increment/NumberFieldIncrement.test.tsx
@@ -4,7 +4,7 @@ import { screen, fireEvent } from '@mui/internal-test-utils';
 import { NumberField } from '@base_ui/react/NumberField';
 import { createRenderer, describeConformance } from '#test-utils';
 import { CHANGE_VALUE_TICK_DELAY, START_AUTO_CHANGE_DELAY } from '../utils/constants';
-import { NumberFieldContext } from '../Root/NumberFieldContext';
+import { NumberFieldRootContext } from '../Root/NumberFieldRootContext';
 
 const testContext = {
   getIncrementButtonProps: (externalProps) => externalProps,
@@ -15,7 +15,7 @@ const testContext = {
     invalid: false,
     readOnly: false,
   },
-} as NumberFieldContext;
+} as NumberFieldRootContext;
 
 describe('<NumberField.Increment />', () => {
   const { render, clock } = createRenderer();
@@ -24,7 +24,9 @@ describe('<NumberField.Increment />', () => {
     refInstanceof: window.HTMLButtonElement,
     render(node) {
       return render(
-        <NumberFieldContext.Provider value={testContext}>{node}</NumberFieldContext.Provider>,
+        <NumberFieldRootContext.Provider value={testContext}>
+          {node}
+        </NumberFieldRootContext.Provider>,
       );
     },
   }));
diff --git a/packages/mui-base/src/NumberField/Increment/NumberFieldIncrement.tsx b/packages/mui-base/src/NumberField/Increment/NumberFieldIncrement.tsx
index 6974a4860..addb79544 100644
--- a/packages/mui-base/src/NumberField/Increment/NumberFieldIncrement.tsx
+++ b/packages/mui-base/src/NumberField/Increment/NumberFieldIncrement.tsx
@@ -1,7 +1,7 @@
 'use client';
 import * as React from 'react';
 import PropTypes from 'prop-types';
-import { useNumberFieldContext } from '../Root/NumberFieldContext';
+import { useNumberFieldRootContext } from '../Root/NumberFieldRootContext';
 import { useComponentRenderer } from '../../utils/useComponentRenderer';
 import type { NumberFieldRoot } from '../Root/NumberFieldRoot';
 import type { BaseUIComponentProps } from '../../utils/types';
@@ -23,7 +23,7 @@ const NumberFieldIncrement = React.forwardRef(function NumberFieldIncrement(
 ) {
   const { render, className, ...otherProps } = props;
 
-  const { getIncrementButtonProps, ownerState } = useNumberFieldContext('Increment');
+  const { getIncrementButtonProps, ownerState } = useNumberFieldRootContext();
 
   const { renderElement } = useComponentRenderer({
     propGetter: getIncrementButtonProps,
diff --git a/packages/mui-base/src/NumberField/Input/NumberFieldInput.test.tsx b/packages/mui-base/src/NumberField/Input/NumberFieldInput.test.tsx
index 46ef5531e..ffa6e1348 100644
--- a/packages/mui-base/src/NumberField/Input/NumberFieldInput.test.tsx
+++ b/packages/mui-base/src/NumberField/Input/NumberFieldInput.test.tsx
@@ -3,7 +3,7 @@ import { expect } from 'chai';
 import { act, screen, fireEvent } from '@mui/internal-test-utils';
 import { NumberField } from '@base_ui/react/NumberField';
 import { createRenderer, describeConformance } from '#test-utils';
-import { NumberFieldContext } from '../Root/NumberFieldContext';
+import { NumberFieldRootContext } from '../Root/NumberFieldRootContext';
 
 const testContext = {
   getInputProps: (externalProps) => externalProps,
@@ -14,7 +14,7 @@ const testContext = {
     invalid: false,
     readOnly: false,
   },
-} as NumberFieldContext;
+} as NumberFieldRootContext;
 
 describe('<NumberField.Input />', () => {
   const { render } = createRenderer();
@@ -23,7 +23,9 @@ describe('<NumberField.Input />', () => {
     refInstanceof: window.HTMLInputElement,
     render(node) {
       return render(
-        <NumberFieldContext.Provider value={testContext}>{node}</NumberFieldContext.Provider>,
+        <NumberFieldRootContext.Provider value={testContext}>
+          {node}
+        </NumberFieldRootContext.Provider>,
       );
     },
   }));
diff --git a/packages/mui-base/src/NumberField/Input/NumberFieldInput.tsx b/packages/mui-base/src/NumberField/Input/NumberFieldInput.tsx
index d714fcedb..8638b289b 100644
--- a/packages/mui-base/src/NumberField/Input/NumberFieldInput.tsx
+++ b/packages/mui-base/src/NumberField/Input/NumberFieldInput.tsx
@@ -1,7 +1,7 @@
 'use client';
 import * as React from 'react';
 import PropTypes from 'prop-types';
-import { useNumberFieldContext } from '../Root/NumberFieldContext';
+import { useNumberFieldRootContext } from '../Root/NumberFieldRootContext';
 import { useComponentRenderer } from '../../utils/useComponentRenderer';
 import { useForkRef } from '../../utils/useForkRef';
 import type { NumberFieldRoot } from '../Root/NumberFieldRoot';
@@ -24,7 +24,7 @@ const NumberFieldInput = React.forwardRef(function NumberFieldInput(
 ) {
   const { render, className, ...otherProps } = props;
 
-  const { getInputProps, inputRef, ownerState } = useNumberFieldContext('Input');
+  const { getInputProps, inputRef, ownerState } = useNumberFieldRootContext();
 
   const mergedInputRef = useForkRef(forwardedRef, inputRef);
 
diff --git a/packages/mui-base/src/NumberField/Root/NumberFieldContext.ts b/packages/mui-base/src/NumberField/Root/NumberFieldContext.ts
deleted file mode 100644
index 3dbd2becb..000000000
--- a/packages/mui-base/src/NumberField/Root/NumberFieldContext.ts
+++ /dev/null
@@ -1,24 +0,0 @@
-'use client';
-import * as React from 'react';
-import type { UseNumberFieldRoot } from './useNumberFieldRoot';
-import type { NumberFieldRoot } from './NumberFieldRoot';
-
-export interface NumberFieldContext extends UseNumberFieldRoot.ReturnValue {
-  ownerState: NumberFieldRoot.OwnerState;
-}
-
-export const NumberFieldContext = React.createContext<NumberFieldContext | null>(null);
-
-if (process.env.NODE_ENV !== 'production') {
-  NumberFieldContext.displayName = 'NumberFieldContext';
-}
-
-type Part = 'Group' | 'Input' | 'Increment' | 'Decrement' | 'ScrubArea' | 'ScrubAreaCursor';
-
-export function useNumberFieldContext(part: Part) {
-  const context = React.useContext(NumberFieldContext);
-  if (context === null) {
-    throw new Error(`Base UI: NumberField${part} is not placed inside the NumberField component.`);
-  }
-  return context;
-}
diff --git a/packages/mui-base/src/NumberField/Root/NumberFieldRoot.tsx b/packages/mui-base/src/NumberField/Root/NumberFieldRoot.tsx
index fb5bce021..1e8132eca 100644
--- a/packages/mui-base/src/NumberField/Root/NumberFieldRoot.tsx
+++ b/packages/mui-base/src/NumberField/Root/NumberFieldRoot.tsx
@@ -1,7 +1,7 @@
 'use client';
 import * as React from 'react';
 import PropTypes from 'prop-types';
-import { NumberFieldContext } from './NumberFieldContext';
+import { NumberFieldRootContext } from './NumberFieldRootContext';
 import { UseNumberFieldRoot, useNumberFieldRoot } from './useNumberFieldRoot';
 import { useFieldRootContext } from '../../Field/Root/FieldRootContext';
 import { useComponentRenderer } from '../../utils/useComponentRenderer';
@@ -91,9 +91,9 @@ const NumberFieldRoot = React.forwardRef(function NumberFieldRoot(
   });
 
   return (
-    <NumberFieldContext.Provider value={contextValue}>
+    <NumberFieldRootContext.Provider value={contextValue}>
       {renderElement()}
-    </NumberFieldContext.Provider>
+    </NumberFieldRootContext.Provider>
   );
 });
 
diff --git a/packages/mui-base/src/NumberField/Root/NumberFieldRootContext.ts b/packages/mui-base/src/NumberField/Root/NumberFieldRootContext.ts
new file mode 100644
index 000000000..2da27b527
--- /dev/null
+++ b/packages/mui-base/src/NumberField/Root/NumberFieldRootContext.ts
@@ -0,0 +1,27 @@
+'use client';
+import * as React from 'react';
+import type { UseNumberFieldRoot } from './useNumberFieldRoot';
+import type { NumberFieldRoot } from './NumberFieldRoot';
+
+export interface NumberFieldRootContext extends UseNumberFieldRoot.ReturnValue {
+  ownerState: NumberFieldRoot.OwnerState;
+}
+
+export const NumberFieldRootContext = React.createContext<NumberFieldRootContext | undefined>(
+  undefined,
+);
+
+if (process.env.NODE_ENV !== 'production') {
+  NumberFieldRootContext.displayName = 'NumberFieldRootContext';
+}
+
+export function useNumberFieldRootContext() {
+  const context = React.useContext(NumberFieldRootContext);
+  if (context === undefined) {
+    throw new Error(
+      'Base UI: NumberFieldRootContext is missing. NumberField parts must be placed within <NumberField.Root>.',
+    );
+  }
+
+  return context;
+}
diff --git a/packages/mui-base/src/NumberField/ScrubArea/NumberFieldScrubArea.test.tsx b/packages/mui-base/src/NumberField/ScrubArea/NumberFieldScrubArea.test.tsx
index 26a693730..05b9ba8da 100644
--- a/packages/mui-base/src/NumberField/ScrubArea/NumberFieldScrubArea.test.tsx
+++ b/packages/mui-base/src/NumberField/ScrubArea/NumberFieldScrubArea.test.tsx
@@ -4,7 +4,7 @@ import { screen, waitFor } from '@mui/internal-test-utils';
 import { NumberField } from '@base_ui/react/NumberField';
 import { createRenderer, describeConformance } from '#test-utils';
 import { isWebKit } from '../../utils/detectBrowser';
-import { NumberFieldContext } from '../Root/NumberFieldContext';
+import { NumberFieldRootContext } from '../Root/NumberFieldRootContext';
 
 function createPointerMoveEvent({ movementX = 0, movementY = 0 }) {
   return new PointerEvent('pointermove', {
@@ -23,7 +23,7 @@ const testContext = {
     invalid: false,
     readOnly: false,
   },
-} as NumberFieldContext;
+} as NumberFieldRootContext;
 
 describe('<NumberField.ScrubArea />', () => {
   const { render } = createRenderer();
@@ -32,7 +32,9 @@ describe('<NumberField.ScrubArea />', () => {
     refInstanceof: window.HTMLSpanElement,
     render(node) {
       return render(
-        <NumberFieldContext.Provider value={testContext}>{node}</NumberFieldContext.Provider>,
+        <NumberFieldRootContext.Provider value={testContext}>
+          {node}
+        </NumberFieldRootContext.Provider>,
       );
     },
   }));
diff --git a/packages/mui-base/src/NumberField/ScrubArea/NumberFieldScrubArea.tsx b/packages/mui-base/src/NumberField/ScrubArea/NumberFieldScrubArea.tsx
index e6823be8f..8ed06f68d 100644
--- a/packages/mui-base/src/NumberField/ScrubArea/NumberFieldScrubArea.tsx
+++ b/packages/mui-base/src/NumberField/ScrubArea/NumberFieldScrubArea.tsx
@@ -2,7 +2,7 @@
 import * as React from 'react';
 import PropTypes from 'prop-types';
 import type { BaseUIComponentProps } from '../../utils/types';
-import { useNumberFieldContext } from '../Root/NumberFieldContext';
+import { useNumberFieldRootContext } from '../Root/NumberFieldRootContext';
 import { useComponentRenderer } from '../../utils/useComponentRenderer';
 import { useForkRef } from '../../utils/useForkRef';
 import type { NumberFieldRoot } from '../Root/NumberFieldRoot';
@@ -32,7 +32,7 @@ const NumberFieldScrubArea = React.forwardRef(function NumberFieldScrubArea(
   } = props;
 
   const { getScrubAreaProps, scrubAreaRef, scrubHandleRef, ownerState } =
-    useNumberFieldContext('ScrubArea');
+    useNumberFieldRootContext();
 
   React.useImperativeHandle(scrubHandleRef, () => ({
     direction,
diff --git a/packages/mui-base/src/NumberField/ScrubAreaCursor/NumberFieldScrubAreaCursor.test.tsx b/packages/mui-base/src/NumberField/ScrubAreaCursor/NumberFieldScrubAreaCursor.test.tsx
index de3ef46f0..72d956b20 100644
--- a/packages/mui-base/src/NumberField/ScrubAreaCursor/NumberFieldScrubAreaCursor.test.tsx
+++ b/packages/mui-base/src/NumberField/ScrubAreaCursor/NumberFieldScrubAreaCursor.test.tsx
@@ -4,7 +4,7 @@ import { screen } from '@mui/internal-test-utils';
 import { NumberField } from '@base_ui/react/NumberField';
 import { createRenderer, describeConformance } from '#test-utils';
 import { isWebKit } from '../../utils/detectBrowser';
-import { NumberFieldContext } from '../Root/NumberFieldContext';
+import { NumberFieldRootContext } from '../Root/NumberFieldRootContext';
 
 const testContext = {
   getScrubAreaCursorProps: (externalProps) => externalProps,
@@ -16,7 +16,7 @@ const testContext = {
     invalid: false,
     readOnly: false,
   },
-} as NumberFieldContext;
+} as NumberFieldRootContext;
 
 describe('<NumberField.ScrubAreaCursor />', () => {
   const { render } = createRenderer();
@@ -30,7 +30,9 @@ describe('<NumberField.ScrubAreaCursor />', () => {
     refInstanceof: window.HTMLSpanElement,
     render(node) {
       return render(
-        <NumberFieldContext.Provider value={testContext}>{node}</NumberFieldContext.Provider>,
+        <NumberFieldRootContext.Provider value={testContext}>
+          {node}
+        </NumberFieldRootContext.Provider>,
       );
     },
   }));
diff --git a/packages/mui-base/src/NumberField/ScrubAreaCursor/NumberFieldScrubAreaCursor.tsx b/packages/mui-base/src/NumberField/ScrubAreaCursor/NumberFieldScrubAreaCursor.tsx
index aea53c103..fcf17c3c3 100644
--- a/packages/mui-base/src/NumberField/ScrubAreaCursor/NumberFieldScrubAreaCursor.tsx
+++ b/packages/mui-base/src/NumberField/ScrubAreaCursor/NumberFieldScrubAreaCursor.tsx
@@ -2,7 +2,7 @@
 import * as React from 'react';
 import * as ReactDOM from 'react-dom';
 import PropTypes from 'prop-types';
-import { useNumberFieldContext } from '../Root/NumberFieldContext';
+import { useNumberFieldRootContext } from '../Root/NumberFieldRootContext';
 import { isWebKit } from '../../utils/detectBrowser';
 import { useComponentRenderer } from '../../utils/useComponentRenderer';
 import { useForkRef } from '../../utils/useForkRef';
@@ -28,7 +28,7 @@ const NumberFieldScrubAreaCursor = React.forwardRef(function NumberFieldScrubAre
   const { render, className, ...otherProps } = props;
 
   const { isScrubbing, scrubAreaCursorRef, ownerState, getScrubAreaCursorProps } =
-    useNumberFieldContext('ScrubAreaCursor');
+    useNumberFieldRootContext();
 
   const [element, setElement] = React.useState<Element | null>(null);
 
diff --git a/packages/mui-base/src/Popover/Positioner/PopoverPositionerContext.ts b/packages/mui-base/src/Popover/Positioner/PopoverPositionerContext.ts
index 073694c62..ff3eaae71 100644
--- a/packages/mui-base/src/Popover/Positioner/PopoverPositionerContext.ts
+++ b/packages/mui-base/src/Popover/Positioner/PopoverPositionerContext.ts
@@ -10,14 +10,21 @@ export interface PopoverPositionerContext {
   arrowStyles: React.CSSProperties;
 }
 
-export const PopoverPositionerContext = React.createContext<PopoverPositionerContext | null>(null);
+export const PopoverPositionerContext = React.createContext<PopoverPositionerContext | undefined>(
+  undefined,
+);
+
+if (process.env.NODE_ENV !== 'production') {
+  PopoverPositionerContext.displayName = 'PopoverPositionerContext';
+}
 
 export function usePopoverPositionerContext() {
   const context = React.useContext(PopoverPositionerContext);
-  if (context === null) {
+  if (context === undefined) {
     throw new Error(
-      '<Popover.Popup> and <Popover.Arrow> must be used within the <Popover.Positioner> component',
+      'Base UI: PopoverPositionerContext is missing. PopoverPositioner parts must be placed within <Popover.Positioner>.',
     );
   }
+
   return context;
 }
diff --git a/packages/mui-base/src/Popover/Root/PopoverRootContext.ts b/packages/mui-base/src/Popover/Root/PopoverRootContext.ts
index a6f621d8a..666a129a9 100644
--- a/packages/mui-base/src/Popover/Root/PopoverRootContext.ts
+++ b/packages/mui-base/src/Popover/Root/PopoverRootContext.ts
@@ -28,12 +28,19 @@ export interface PopoverRootContext {
   getRootPopupProps: (externalProps?: GenericHTMLProps) => GenericHTMLProps;
 }
 
-export const PopoverRootContext = React.createContext<PopoverRootContext | null>(null);
+export const PopoverRootContext = React.createContext<PopoverRootContext | undefined>(undefined);
+
+if (process.env.NODE_ENV !== 'production') {
+  PopoverRootContext.displayName = 'PopoverRootContext';
+}
 
 export function usePopoverRootContext() {
   const context = React.useContext(PopoverRootContext);
-  if (context === null) {
-    throw new Error('Popover components must be used within the <Popover.Root> component');
+  if (context === undefined) {
+    throw new Error(
+      'Base UI: PopoverRootContext is missing. Popover parts must be placed within <Popover.Root>.',
+    );
   }
+
   return context;
 }
diff --git a/packages/mui-base/src/PreviewCard/Positioner/PreviewCardPositionerContext.ts b/packages/mui-base/src/PreviewCard/Positioner/PreviewCardPositionerContext.ts
index 842819d6e..3d096866a 100644
--- a/packages/mui-base/src/PreviewCard/Positioner/PreviewCardPositionerContext.ts
+++ b/packages/mui-base/src/PreviewCard/Positioner/PreviewCardPositionerContext.ts
@@ -10,15 +10,21 @@ export interface PreviewCardPositionerContext {
   arrowStyles: React.CSSProperties;
 }
 
-export const PreviewCardPositionerContext =
-  React.createContext<PreviewCardPositionerContext | null>(null);
+export const PreviewCardPositionerContext = React.createContext<
+  PreviewCardPositionerContext | undefined
+>(undefined);
+
+if (process.env.NODE_ENV !== 'production') {
+  PreviewCardPositionerContext.displayName = 'PreviewCardPositionerContext';
+}
 
 export function usePreviewCardPositionerContext() {
   const context = React.useContext(PreviewCardPositionerContext);
-  if (context === null) {
+  if (context === undefined) {
     throw new Error(
       'Base UI: <PreviewCard.Popup> and <PreviewCard.Arrow> must be used within the <PreviewCard.Positioner> component',
     );
   }
+
   return context;
 }
diff --git a/packages/mui-base/src/PreviewCard/Root/PreviewCardContext.ts b/packages/mui-base/src/PreviewCard/Root/PreviewCardContext.ts
index 4e87ed603..337c14021 100644
--- a/packages/mui-base/src/PreviewCard/Root/PreviewCardContext.ts
+++ b/packages/mui-base/src/PreviewCard/Root/PreviewCardContext.ts
@@ -22,12 +22,21 @@ export interface PreviewCardRootContext {
   popupRef: React.RefObject<HTMLElement | null>;
 }
 
-export const PreviewCardRootContext = React.createContext<PreviewCardRootContext | null>(null);
+export const PreviewCardRootContext = React.createContext<PreviewCardRootContext | undefined>(
+  undefined,
+);
+
+if (process.env.NODE_ENV !== 'production') {
+  PreviewCardRootContext.displayName = 'PreviewCardRootContext';
+}
 
 export function usePreviewCardRootContext() {
   const context = React.useContext(PreviewCardRootContext);
-  if (context === null) {
-    throw new Error('PreviewCard components must be used within the <PreviewCard.Root> component');
+  if (context === undefined) {
+    throw new Error(
+      'Base UI: PreviewCardRootContext is missing. PreviewCard parts must be placed within <PreviewCard.Root>.',
+    );
   }
+
   return context;
 }
diff --git a/packages/mui-base/src/Progress/Root/ProgressRootContext.tsx b/packages/mui-base/src/Progress/Root/ProgressRootContext.tsx
index f48eb17bc..029373389 100644
--- a/packages/mui-base/src/Progress/Root/ProgressRootContext.tsx
+++ b/packages/mui-base/src/Progress/Root/ProgressRootContext.tsx
@@ -19,7 +19,10 @@ if (process.env.NODE_ENV !== 'production') {
 export function useProgressRootContext() {
   const context = React.useContext(ProgressRootContext);
   if (context === undefined) {
-    throw new Error('useProgressContext must be used inside a Progress component');
+    throw new Error(
+      'Base UI: ProgressRootContext is missing. Progress parts must be placed within <Progress.Root>.',
+    );
   }
+
   return context;
 }
diff --git a/packages/mui-base/src/Radio/Root/RadioRootContext.ts b/packages/mui-base/src/Radio/Root/RadioRootContext.ts
index 512fd2fed..b419b765d 100644
--- a/packages/mui-base/src/Radio/Root/RadioRootContext.ts
+++ b/packages/mui-base/src/Radio/Root/RadioRootContext.ts
@@ -8,12 +8,19 @@ export interface RadioRootContext {
   required: boolean;
 }
 
-export const RadioRootContext = React.createContext<RadioRootContext | null>(null);
+export const RadioRootContext = React.createContext<RadioRootContext | undefined>(undefined);
+
+if (process.env.NODE_ENV !== 'production') {
+  RadioRootContext.displayName = 'RadioRootContext';
+}
 
 export function useRadioRootContext() {
   const value = React.useContext(RadioRootContext);
-  if (value === null) {
-    throw new Error('Base UI: <Radio.Indicator> must be used within <Radio.Root>');
+  if (value === undefined) {
+    throw new Error(
+      'Base UI: RadioRootContext is missing. Radio parts must be placed within <Radio.Root>.',
+    );
   }
+
   return value;
 }
diff --git a/packages/mui-base/src/RadioGroup/Root/RadioGroupRootContext.ts b/packages/mui-base/src/RadioGroup/Root/RadioGroupRootContext.ts
index 2aef2556e..73fe30970 100644
--- a/packages/mui-base/src/RadioGroup/Root/RadioGroupRootContext.ts
+++ b/packages/mui-base/src/RadioGroup/Root/RadioGroupRootContext.ts
@@ -24,6 +24,10 @@ export const RadioGroupRootContext = React.createContext<RadioGroupRootContext>(
   setTouched: NOOP,
 });
 
+if (process.env.NODE_ENV !== 'production') {
+  RadioGroupRootContext.displayName = 'RadioGroupRootContext';
+}
+
 export function useRadioGroupRootContext() {
   return React.useContext(RadioGroupRootContext);
 }
diff --git a/packages/mui-base/src/Slider/Control/SliderControl.test.tsx b/packages/mui-base/src/Slider/Control/SliderControl.test.tsx
index 6fd286664..14c3b7981 100644
--- a/packages/mui-base/src/Slider/Control/SliderControl.test.tsx
+++ b/packages/mui-base/src/Slider/Control/SliderControl.test.tsx
@@ -1,11 +1,10 @@
 import * as React from 'react';
 import { Slider } from '@base_ui/react/Slider';
 import { createRenderer, describeConformance } from '#test-utils';
-import { SliderContext } from '../Root/SliderContext';
-import type { SliderRoot } from '../Root/SliderRoot';
+import { SliderRootContext } from '../Root/SliderRootContext';
 import { NOOP } from '../../utils/noop';
 
-const testRootContext: SliderRoot.Context = {
+const testRootContext: SliderRootContext = {
   active: -1,
   areValuesEqual: () => true,
   axis: 'horizontal',
@@ -59,7 +58,7 @@ describe('<Slider.Control />', () => {
   describeConformance(<Slider.Control />, () => ({
     render: (node) => {
       return render(
-        <SliderContext.Provider value={testRootContext}>{node}</SliderContext.Provider>,
+        <SliderRootContext.Provider value={testRootContext}>{node}</SliderRootContext.Provider>,
       );
     },
     refInstanceof: window.HTMLSpanElement,
diff --git a/packages/mui-base/src/Slider/Control/SliderControl.tsx b/packages/mui-base/src/Slider/Control/SliderControl.tsx
index 3622e1692..6d4cb09d8 100644
--- a/packages/mui-base/src/Slider/Control/SliderControl.tsx
+++ b/packages/mui-base/src/Slider/Control/SliderControl.tsx
@@ -3,7 +3,7 @@ import * as React from 'react';
 import PropTypes from 'prop-types';
 import type { BaseUIComponentProps } from '../../utils/types';
 import { useComponentRenderer } from '../../utils/useComponentRenderer';
-import { useSliderContext } from '../Root/SliderContext';
+import { useSliderRootContext } from '../Root/SliderRootContext';
 import { sliderStyleHookMapping } from '../Root/styleHooks';
 import type { SliderRoot } from '../Root/SliderRoot';
 import { useSliderControl } from './useSliderControl';
@@ -39,7 +39,7 @@ const SliderControl = React.forwardRef(function SliderControl(
     setValueState,
     step,
     thumbRefs,
-  } = useSliderContext();
+  } = useSliderRootContext();
 
   const { getRootProps } = useSliderControl({
     areValuesEqual,
diff --git a/packages/mui-base/src/Slider/Indicator/SliderIndicator.test.tsx b/packages/mui-base/src/Slider/Indicator/SliderIndicator.test.tsx
index 658c9a54f..842d83fd7 100644
--- a/packages/mui-base/src/Slider/Indicator/SliderIndicator.test.tsx
+++ b/packages/mui-base/src/Slider/Indicator/SliderIndicator.test.tsx
@@ -1,11 +1,10 @@
 import * as React from 'react';
 import { Slider } from '@base_ui/react/Slider';
 import { createRenderer, describeConformance } from '#test-utils';
-import { SliderContext } from '../Root/SliderContext';
-import type { SliderRoot } from '../Root/SliderRoot';
+import { SliderRootContext } from '../Root/SliderRootContext';
 import { NOOP } from '../../utils/noop';
 
-const testRootContext: SliderRoot.Context = {
+const testRootContext: SliderRootContext = {
   active: -1,
   areValuesEqual: () => true,
   axis: 'horizontal',
@@ -59,7 +58,7 @@ describe('<Slider.Indicator />', () => {
   describeConformance(<Slider.Indicator />, () => ({
     render: (node) => {
       return render(
-        <SliderContext.Provider value={testRootContext}>{node}</SliderContext.Provider>,
+        <SliderRootContext.Provider value={testRootContext}>{node}</SliderRootContext.Provider>,
       );
     },
     refInstanceof: window.HTMLSpanElement,
diff --git a/packages/mui-base/src/Slider/Indicator/SliderIndicator.tsx b/packages/mui-base/src/Slider/Indicator/SliderIndicator.tsx
index e28914e3f..aec14a707 100644
--- a/packages/mui-base/src/Slider/Indicator/SliderIndicator.tsx
+++ b/packages/mui-base/src/Slider/Indicator/SliderIndicator.tsx
@@ -3,7 +3,7 @@ import * as React from 'react';
 import PropTypes from 'prop-types';
 import type { BaseUIComponentProps } from '../../utils/types';
 import { useComponentRenderer } from '../../utils/useComponentRenderer';
-import { useSliderContext } from '../Root/SliderContext';
+import { useSliderRootContext } from '../Root/SliderRootContext';
 import { sliderStyleHookMapping } from '../Root/styleHooks';
 import type { SliderRoot } from '../Root/SliderRoot';
 import { useSliderIndicator } from './useSliderIndicator';
@@ -24,7 +24,7 @@ const SliderIndicator = React.forwardRef(function SliderIndicator(
   const { render, className, ...otherProps } = props;
 
   const { axis, direction, disabled, orientation, ownerState, percentageValues } =
-    useSliderContext();
+    useSliderRootContext();
 
   const { getRootProps } = useSliderIndicator({
     axis,
diff --git a/packages/mui-base/src/Slider/Output/SliderOutput.test.tsx b/packages/mui-base/src/Slider/Output/SliderOutput.test.tsx
index 500877d60..a223875a0 100644
--- a/packages/mui-base/src/Slider/Output/SliderOutput.test.tsx
+++ b/packages/mui-base/src/Slider/Output/SliderOutput.test.tsx
@@ -2,11 +2,10 @@ import * as React from 'react';
 import { expect } from 'chai';
 import { Slider } from '@base_ui/react/Slider';
 import { createRenderer, describeConformance } from '#test-utils';
-import { SliderContext } from '../Root/SliderContext';
+import { SliderRootContext } from '../Root/SliderRootContext';
 import { NOOP } from '../../utils/noop';
-import type { SliderRoot } from '../Root/SliderRoot';
 
-const testRootContext: SliderRoot.Context = {
+const testRootContext: SliderRootContext = {
   active: -1,
   areValuesEqual: () => true,
   axis: 'horizontal',
@@ -60,7 +59,7 @@ describe('<Slider.Output />', () => {
   describeConformance(<Slider.Output />, () => ({
     render: (node) => {
       return render(
-        <SliderContext.Provider value={testRootContext}>{node}</SliderContext.Provider>,
+        <SliderRootContext.Provider value={testRootContext}>{node}</SliderRootContext.Provider>,
       );
     },
     refInstanceof: window.HTMLOutputElement,
diff --git a/packages/mui-base/src/Slider/Output/SliderOutput.tsx b/packages/mui-base/src/Slider/Output/SliderOutput.tsx
index a2d80a44e..e2a306cfc 100644
--- a/packages/mui-base/src/Slider/Output/SliderOutput.tsx
+++ b/packages/mui-base/src/Slider/Output/SliderOutput.tsx
@@ -3,7 +3,7 @@ import * as React from 'react';
 import PropTypes from 'prop-types';
 import type { BaseUIComponentProps } from '../../utils/types';
 import { useComponentRenderer } from '../../utils/useComponentRenderer';
-import { useSliderContext } from '../Root/SliderContext';
+import { useSliderRootContext } from '../Root/SliderRootContext';
 import { sliderStyleHookMapping } from '../Root/styleHooks';
 import type { SliderRoot } from '../Root/SliderRoot';
 import { useSliderOutput } from './useSliderOutput';
@@ -23,7 +23,7 @@ const SliderOutput = React.forwardRef(function SliderOutput(
 ) {
   const { render, className, ...otherProps } = props;
 
-  const { inputIdMap, ownerState, values } = useSliderContext();
+  const { inputIdMap, ownerState, values } = useSliderRootContext();
 
   const { getRootProps } = useSliderOutput({
     inputIdMap,
diff --git a/packages/mui-base/src/Slider/Root/SliderContext.tsx b/packages/mui-base/src/Slider/Root/SliderContext.tsx
deleted file mode 100644
index 33cb14bfe..000000000
--- a/packages/mui-base/src/Slider/Root/SliderContext.tsx
+++ /dev/null
@@ -1,20 +0,0 @@
-'use client';
-import * as React from 'react';
-import type { SliderRoot } from './SliderRoot';
-
-/**
- * @ignore - internal component.
- */
-export const SliderContext = React.createContext<SliderRoot.Context | undefined>(undefined);
-
-if (process.env.NODE_ENV !== 'production') {
-  SliderContext.displayName = 'SliderContext';
-}
-
-export function useSliderContext() {
-  const context = React.useContext(SliderContext);
-  if (context === undefined) {
-    throw new Error('useSliderContext must be used inside a Slider component');
-  }
-  return context;
-}
diff --git a/packages/mui-base/src/Slider/Root/SliderRoot.tsx b/packages/mui-base/src/Slider/Root/SliderRoot.tsx
index 274855b2a..0346f83f6 100644
--- a/packages/mui-base/src/Slider/Root/SliderRoot.tsx
+++ b/packages/mui-base/src/Slider/Root/SliderRoot.tsx
@@ -7,8 +7,9 @@ import type { FieldRoot } from '../../Field/Root/FieldRoot';
 import { CompositeList } from '../../Composite/List/CompositeList';
 import { sliderStyleHookMapping } from './styleHooks';
 import { useSliderRoot } from './useSliderRoot';
-import { SliderContext } from './SliderContext';
+import { SliderRootContext } from './SliderRootContext';
 import { useFieldRootContext } from '../../Field/Root/FieldRootContext';
+
 /**
  *
  * Demos:
@@ -104,18 +105,13 @@ const SliderRoot = React.forwardRef(function SliderRoot(
   });
 
   return (
-    <SliderContext.Provider value={contextValue}>
+    <SliderRootContext.Provider value={contextValue}>
       <CompositeList elementsRef={slider.thumbRefs}>{renderElement()}</CompositeList>
-    </SliderContext.Provider>
+    </SliderRootContext.Provider>
   );
 });
 
 export namespace SliderRoot {
-  export interface Context
-    extends Omit<useSliderRoot.ReturnValue, 'compoundComponentContextValue' | 'getRootProps'> {
-    ownerState: OwnerState;
-  }
-
   export interface OwnerState extends FieldRoot.OwnerState {
     /**
      * The index of the active thumb.
diff --git a/packages/mui-base/src/Slider/Root/SliderRootContext.ts b/packages/mui-base/src/Slider/Root/SliderRootContext.ts
new file mode 100644
index 000000000..60e7e613a
--- /dev/null
+++ b/packages/mui-base/src/Slider/Root/SliderRootContext.ts
@@ -0,0 +1,24 @@
+'use client';
+import * as React from 'react';
+import type { SliderRoot } from './SliderRoot';
+import type { useSliderRoot } from './useSliderRoot';
+
+export interface SliderRootContext extends Omit<useSliderRoot.ReturnValue, 'getRootProps'> {
+  ownerState: SliderRoot.OwnerState;
+}
+
+export const SliderRootContext = React.createContext<SliderRootContext | undefined>(undefined);
+
+if (process.env.NODE_ENV !== 'production') {
+  SliderRootContext.displayName = 'SliderRootContext';
+}
+
+export function useSliderRootContext() {
+  const context = React.useContext(SliderRootContext);
+  if (context === undefined) {
+    throw new Error(
+      'Base UI: SliderRootContext is missing. Slider parts must be placed within <Slider.Root>.',
+    );
+  }
+  return context;
+}
diff --git a/packages/mui-base/src/Slider/Thumb/SliderThumb.test.tsx b/packages/mui-base/src/Slider/Thumb/SliderThumb.test.tsx
index ac6512002..c6d8a78e3 100644
--- a/packages/mui-base/src/Slider/Thumb/SliderThumb.test.tsx
+++ b/packages/mui-base/src/Slider/Thumb/SliderThumb.test.tsx
@@ -1,11 +1,10 @@
 import * as React from 'react';
 import { Slider } from '@base_ui/react/Slider';
 import { createRenderer, describeConformance } from '#test-utils';
-import { SliderContext } from '../Root/SliderContext';
+import { SliderRootContext } from '../Root/SliderRootContext';
 import { NOOP } from '../../utils/noop';
-import type { SliderRoot } from '../Root/SliderRoot';
 
-const testRootContext: SliderRoot.Context = {
+const testRootContext: SliderRootContext = {
   active: -1,
   areValuesEqual: () => true,
   axis: 'horizontal',
@@ -59,7 +58,7 @@ describe('<Slider.Thumb />', () => {
   describeConformance(<Slider.Thumb />, () => ({
     render: (node) => {
       return render(
-        <SliderContext.Provider value={testRootContext}>{node}</SliderContext.Provider>,
+        <SliderRootContext.Provider value={testRootContext}>{node}</SliderRootContext.Provider>,
       );
     },
     refInstanceof: window.HTMLSpanElement,
diff --git a/packages/mui-base/src/Slider/Thumb/SliderThumb.tsx b/packages/mui-base/src/Slider/Thumb/SliderThumb.tsx
index c9dc22214..06d8600a8 100644
--- a/packages/mui-base/src/Slider/Thumb/SliderThumb.tsx
+++ b/packages/mui-base/src/Slider/Thumb/SliderThumb.tsx
@@ -7,7 +7,7 @@ import { resolveClassName } from '../../utils/resolveClassName';
 import { BaseUIComponentProps } from '../../utils/types';
 import { useForkRef } from '../../utils/useForkRef';
 import type { SliderRoot } from '../Root/SliderRoot';
-import { useSliderContext } from '../Root/SliderContext';
+import { useSliderRootContext } from '../Root/SliderRootContext';
 import { useSliderThumb } from './useSliderThumb';
 import { isReactVersionAtLeast } from '../../utils/reactVersion';
 
@@ -70,7 +70,7 @@ const SliderThumb = React.forwardRef(function SliderThumb(
     step,
     tabIndex,
     values,
-  } = useSliderContext();
+  } = useSliderRootContext();
 
   let renderPropRef = null;
   if (typeof render !== 'function') {
diff --git a/packages/mui-base/src/Slider/Track/SliderTrack.test.tsx b/packages/mui-base/src/Slider/Track/SliderTrack.test.tsx
index 88165fc91..bfbda1262 100644
--- a/packages/mui-base/src/Slider/Track/SliderTrack.test.tsx
+++ b/packages/mui-base/src/Slider/Track/SliderTrack.test.tsx
@@ -1,11 +1,10 @@
 import * as React from 'react';
 import { Slider } from '@base_ui/react/Slider';
 import { createRenderer, describeConformance } from '#test-utils';
-import { SliderContext } from '../Root/SliderContext';
+import { SliderRootContext } from '../Root/SliderRootContext';
 import { NOOP } from '../../utils/noop';
-import type { SliderRoot } from '../Root/SliderRoot';
 
-const testRootContext: SliderRoot.Context = {
+const testRootContext: SliderRootContext = {
   active: -1,
   areValuesEqual: () => true,
   axis: 'horizontal',
@@ -59,7 +58,7 @@ describe('<Slider.Track />', () => {
   describeConformance(<Slider.Track />, () => ({
     render: (node) => {
       return render(
-        <SliderContext.Provider value={testRootContext}>{node}</SliderContext.Provider>,
+        <SliderRootContext.Provider value={testRootContext}>{node}</SliderRootContext.Provider>,
       );
     },
     refInstanceof: window.HTMLSpanElement,
diff --git a/packages/mui-base/src/Slider/Track/SliderTrack.tsx b/packages/mui-base/src/Slider/Track/SliderTrack.tsx
index 7fa0de221..4f6c42655 100644
--- a/packages/mui-base/src/Slider/Track/SliderTrack.tsx
+++ b/packages/mui-base/src/Slider/Track/SliderTrack.tsx
@@ -3,7 +3,7 @@ import * as React from 'react';
 import PropTypes from 'prop-types';
 import { BaseUIComponentProps } from '../../utils/types';
 import { useComponentRenderer } from '../../utils/useComponentRenderer';
-import { useSliderContext } from '../Root/SliderContext';
+import { useSliderRootContext } from '../Root/SliderRootContext';
 import type { SliderRoot } from '../Root/SliderRoot';
 import { sliderStyleHookMapping } from '../Root/styleHooks';
 /**
@@ -22,7 +22,7 @@ const SliderTrack = React.forwardRef(function SliderTrack(
 ) {
   const { render, className, ...otherProps } = props;
 
-  const { ownerState } = useSliderContext();
+  const { ownerState } = useSliderRootContext();
 
   const { renderElement } = useComponentRenderer({
     render: render ?? 'span',
diff --git a/packages/mui-base/src/Switch/Root/SwitchRootContext.ts b/packages/mui-base/src/Switch/Root/SwitchRootContext.ts
index 3804b912d..ab61d0653 100644
--- a/packages/mui-base/src/Switch/Root/SwitchRootContext.ts
+++ b/packages/mui-base/src/Switch/Root/SwitchRootContext.ts
@@ -5,10 +5,16 @@ export type SwitchRootContext = SwitchRoot.OwnerState;
 
 export const SwitchRootContext = React.createContext<SwitchRootContext | undefined>(undefined);
 
+if (process.env.NODE_ENV !== 'production') {
+  SwitchRootContext.displayName = 'SwitchRootContext';
+}
+
 export function useSwitchRootContext() {
   const context = React.useContext(SwitchRootContext);
   if (context === undefined) {
-    throw new Error('useSwitchRootContext must be used within a SwitchRootProvider');
+    throw new Error(
+      'Base UI: SwitchRootContext is missing. Switch parts must be placed within <Switch.Root>.',
+    );
   }
 
   return context;
diff --git a/packages/mui-base/src/Tabs/Root/TabsRootContext.ts b/packages/mui-base/src/Tabs/Root/TabsRootContext.ts
index ea4d9101c..ac011c009 100644
--- a/packages/mui-base/src/Tabs/Root/TabsRootContext.ts
+++ b/packages/mui-base/src/Tabs/Root/TabsRootContext.ts
@@ -46,7 +46,7 @@ export interface TabsRootContext {
 /**
  * @ignore - internal component.
  */
-const TabsRootContext = React.createContext<TabsRootContext | null>(null);
+const TabsRootContext = React.createContext<TabsRootContext | undefined>(undefined);
 
 if (process.env.NODE_ENV !== 'production') {
   TabsRootContext.displayName = 'TabsRootContext';
@@ -54,8 +54,10 @@ if (process.env.NODE_ENV !== 'production') {
 
 export function useTabsRootContext() {
   const context = React.useContext(TabsRootContext);
-  if (context == null) {
-    throw new Error('Base UI: No TabsRootContext provided');
+  if (context === undefined) {
+    throw new Error(
+      'Base UI: TabsRootContext is missing. Tabs parts must be placed within <Tabs.Root>.',
+    );
   }
 
   return context;
diff --git a/packages/mui-base/src/Tabs/TabsList/TabsListContext.ts b/packages/mui-base/src/Tabs/TabsList/TabsListContext.ts
index 9b2833529..fa31ac8a9 100644
--- a/packages/mui-base/src/Tabs/TabsList/TabsListContext.ts
+++ b/packages/mui-base/src/Tabs/TabsList/TabsListContext.ts
@@ -9,10 +9,16 @@ export interface TabsListContext {
 
 export const TabsListContext = React.createContext<TabsListContext | undefined>(undefined);
 
+if (process.env.NODE_ENV !== 'production') {
+  TabsListContext.displayName = 'TabsListContext';
+}
+
 export function useTabsListContext() {
   const context = React.useContext(TabsListContext);
   if (context === undefined) {
-    throw new Error('useTabsListContext must be used within a TabsList component');
+    throw new Error(
+      'Base UI: TabsListContext is missing. TabsList parts must be placed within <Tabs.List>.',
+    );
   }
 
   return context;
diff --git a/packages/mui-base/src/Tooltip/Positioner/TooltipPositionerContext.ts b/packages/mui-base/src/Tooltip/Positioner/TooltipPositionerContext.ts
index 6792c3cb5..f3b1dab4c 100644
--- a/packages/mui-base/src/Tooltip/Positioner/TooltipPositionerContext.ts
+++ b/packages/mui-base/src/Tooltip/Positioner/TooltipPositionerContext.ts
@@ -11,13 +11,19 @@ export interface TooltipPositionerContext {
   arrowStyles: React.CSSProperties;
 }
 
-export const TooltipPositionerContext = React.createContext<TooltipPositionerContext | null>(null);
+export const TooltipPositionerContext = React.createContext<TooltipPositionerContext | undefined>(
+  undefined,
+);
+
+if (process.env.NODE_ENV !== 'production') {
+  TooltipPositionerContext.displayName = 'TooltipPositionerContext';
+}
 
 export function useTooltipPositionerContext() {
   const context = React.useContext(TooltipPositionerContext);
-  if (context === null) {
+  if (context === undefined) {
     throw new Error(
-      '<Tooltip.Popup> and <Tooltip.Arrow> must be used within the <Tooltip.Positioner> component',
+      'Base UI: TooltipPositionerContext is missing. TooltipPositioner parts must be placed within <Tooltip.Positioner>.',
     );
   }
   return context;
diff --git a/packages/mui-base/src/Tooltip/Root/TooltipRootContext.ts b/packages/mui-base/src/Tooltip/Root/TooltipRootContext.ts
index 05e581963..8daa11124 100644
--- a/packages/mui-base/src/Tooltip/Root/TooltipRootContext.ts
+++ b/packages/mui-base/src/Tooltip/Root/TooltipRootContext.ts
@@ -24,12 +24,15 @@ export interface TooltipRootContext {
   transitionStatus: TransitionStatus;
 }
 
-export const TooltipRootContext = React.createContext<TooltipRootContext | null>(null);
+export const TooltipRootContext = React.createContext<TooltipRootContext | undefined>(undefined);
 
 export function useTooltipRootContext() {
   const context = React.useContext(TooltipRootContext);
-  if (context === null) {
-    throw new Error('Tooltip components must be used within the <Tooltip.Root> component');
+  if (context === undefined) {
+    throw new Error(
+      'Base UI: TooltipRootContext is missing. Tooltip parts must be placed within <Tooltip.Root>.',
+    );
   }
+
   return context;
 }