diff --git a/include/substrait-mlir/Dialect/Substrait/IR/Substrait.h b/include/substrait-mlir/Dialect/Substrait/IR/Substrait.h
index 710e8539..1d5a602e 100644
--- a/include/substrait-mlir/Dialect/Substrait/IR/Substrait.h
+++ b/include/substrait-mlir/Dialect/Substrait/IR/Substrait.h
@@ -15,19 +15,38 @@
 #include "mlir/IR/SymbolTable.h"                  // IWYU: keep
 #include "mlir/Interfaces/InferTypeOpInterface.h" // IWYU: keep
 
-#include "substrait-mlir/Dialect/Substrait/IR/SubstraitEnums.h.inc" // IWYU: export
+//===----------------------------------------------------------------------===//
+// Substrait dialect
+//===----------------------------------------------------------------------===//
 
 #include "substrait-mlir/Dialect/Substrait/IR/SubstraitOpsDialect.h.inc" // IWYU: export
 
-#include "substrait-mlir/Dialect/Substrait/IR/SubstraitOpInterfaces.h.inc" // IWYU: export
-#include "substrait-mlir/Dialect/Substrait/IR/SubstraitTypeInterfaces.h.inc" // IWYU: export
+//===----------------------------------------------------------------------===//
+// Substrait enums
+//===----------------------------------------------------------------------===//
+
+#include "substrait-mlir/Dialect/Substrait/IR/SubstraitEnums.h.inc" // IWYU: export
+
+//===----------------------------------------------------------------------===//
+// Substrait types
+//===----------------------------------------------------------------------===//
 
+#include "substrait-mlir/Dialect/Substrait/IR/SubstraitTypeInterfaces.h.inc" // IWYU: export
 #define GET_TYPEDEF_CLASSES
 #include "substrait-mlir/Dialect/Substrait/IR/SubstraitOpsTypes.h.inc" // IWYU: export
 
+//===----------------------------------------------------------------------===//
+// Substrait attributes
+//===----------------------------------------------------------------------===//
+
 #define GET_ATTRDEF_CLASSES
 #include "substrait-mlir/Dialect/Substrait/IR/SubstraitOpsAttrs.h.inc" // IWYU: export
 
+//===----------------------------------------------------------------------===//
+// Substrait ops
+//===----------------------------------------------------------------------===//
+
+#include "substrait-mlir/Dialect/Substrait/IR/SubstraitOpInterfaces.h.inc" // IWYU: export
 #define GET_OP_CLASSES
 #include "substrait-mlir/Dialect/Substrait/IR/SubstraitOps.h.inc" // IWYU: export
 
diff --git a/include/substrait-mlir/Dialect/Substrait/IR/SubstraitInterfaces.td b/include/substrait-mlir/Dialect/Substrait/IR/SubstraitInterfaces.td
index 141d1a5a..1c6f795c 100644
--- a/include/substrait-mlir/Dialect/Substrait/IR/SubstraitInterfaces.td
+++ b/include/substrait-mlir/Dialect/Substrait/IR/SubstraitInterfaces.td
@@ -21,6 +21,26 @@ def Substrait_ExpressionOpInterface : OpInterface<"ExpressionOpInterface"> {
   let cppNamespace = "::mlir::substrait";
 }
 
+def Substrait_ExtensibleOpInterface : OpInterface<"ExtensibleOpInterface"> {
+  let description = [{
+    Interface for ops with the `advanced_extension` attribute. Several relations
+    and other message types of the Substrait specification have a field with the
+    same name (or the variant `advanced_extensions`, which has the same meaning)
+    and the interface enables handling all of them transparently.
+  }];
+  let cppNamespace = "::mlir::substrait";
+  let methods = [
+    InterfaceMethod<
+      "Get the `advanced_extension` attribute",
+      "std::optional<::mlir::substrait::AdvancedExtensionAttr>",
+      "getAdvancedExtension">,
+    InterfaceMethod<
+      "Get the `advanced_extension` attribute",
+      "void", "setAdvancedExtensionAttr",
+      (ins "::mlir::substrait::AdvancedExtensionAttr":$attr)>,
+    ];
+}
+
 def Substrait_RelOpInterface : OpInterface<"RelOpInterface"> {
   let description = [{
     Interface for any relational operation in a Substrait plan. This corresponds
diff --git a/include/substrait-mlir/Dialect/Substrait/IR/SubstraitOps.td b/include/substrait-mlir/Dialect/Substrait/IR/SubstraitOps.td
index ad33a1c1..98afce96 100644
--- a/include/substrait-mlir/Dialect/Substrait/IR/SubstraitOps.td
+++ b/include/substrait-mlir/Dialect/Substrait/IR/SubstraitOps.td
@@ -150,6 +150,7 @@ def PlanBodyOp : AnyOf<[
 
 def Substrait_PlanOp : Substrait_Op<"plan", [
     DeclareOpInterfaceMethods<OpAsmOpInterface, ["getDefaultDialect"]>,
+    DeclareOpInterfaceMethods<Substrait_ExtensibleOpInterface>,
     NoTerminator, NoRegionArguments, SingleBlock, SymbolTable
   ]> {
   let summary = "Represents a Substrait plan";
@@ -177,9 +178,13 @@ def Substrait_PlanOp : Substrait_Op<"plan", [
   let builders = [
       OpBuilder<(ins "uint32_t":$major, "uint32_t":$minor, "uint32_t":$patch), [{
         build($_builder, $_state, major, minor, patch,
-              /*git_hash=*/StringAttr(), /*producer*/StringAttr(),
+              /*git_hash=*/"", /*producer*/"");
+      }]>,
+      OpBuilder<(ins "uint32_t":$major, "uint32_t":$minor, "uint32_t":$patch,
+                     "std::string":$git_hash, "std::string":$producer), [{
+        build($_builder, $_state, major, minor, patch, git_hash, producer,
               /*advanced_extension=*/AdvancedExtensionAttr());
-      }]>
+      }]>,
     ];
   let extraClassDefinition = [{
     /// Implement OpAsmOpInterface.
@@ -526,6 +531,7 @@ def Substrait_NamedTableOp : Substrait_RelOp<"named_table", [
 
 def Substrait_ProjectOp : Substrait_RelOp<"project", [
     SingleBlockImplicitTerminator<"::mlir::substrait::YieldOp">,
+    DeclareOpInterfaceMethods<Substrait_ExtensibleOpInterface>,
     DeclareOpInterfaceMethods<OpAsmOpInterface, ["getDefaultDialect"]>
   ]> {
   let summary = "Project operation";
@@ -550,14 +556,18 @@ def Substrait_ProjectOp : Substrait_RelOp<"project", [
     }
     ```
   }];
-  let arguments = (ins Substrait_Relation:$input);
+  let arguments = (ins
+    Substrait_Relation:$input,
+    OptionalAttr<Substrait_AdvancedExtensionAttr>:$advanced_extension
+  );
   let regions = (region AnyRegion:$expressions);
   let results = (outs Substrait_Relation:$result);
   // TODO(ingomueller): We could elide/shorten the block argument from the
   //                    assembly by writing custom printers/parsers similar to
   //                    `scf.for` etc.
   let assemblyFormat = [{
-    $input attr-dict `:` type($input) `->` type($result) $expressions
+    $input (`advanced_extension` `` $advanced_extension^)?
+    attr-dict `:` type($input) `->` type($result) $expressions
   }];
   let hasRegionVerifier = 1;
   let hasFolder = 1;
diff --git a/lib/Target/SubstraitPB/Export.cpp b/lib/Target/SubstraitPB/Export.cpp
index 5373fd29..7cef1839 100644
--- a/lib/Target/SubstraitPB/Export.cpp
+++ b/lib/Target/SubstraitPB/Export.cpp
@@ -23,6 +23,7 @@
 
 using namespace mlir;
 using namespace mlir::substrait;
+using namespace mlir::substrait::protobuf_utils;
 using namespace ::substrait;
 using namespace ::substrait::proto;
 
@@ -59,6 +60,8 @@ class SubstraitExporter {
   DECLARE_EXPORT_FUNC(RelOpInterface, Rel)
   DECLARE_EXPORT_FUNC(SetOp, Rel)
 
+  template <typename MessageType>
+  void exportAdvancedExtension(ExtensibleOpInterface op, MessageType &message);
   std::unique_ptr<pb::Any> exportAny(StringAttr attr);
   FailureOr<std::unique_ptr<pb::Message>> exportOperation(Operation *op);
   FailureOr<std::unique_ptr<proto::Type>> exportType(Location loc,
@@ -90,6 +93,36 @@ class SubstraitExporter {
   std::unique_ptr<SymbolTable> symbolTable;     // Symbol table cache.
 };
 
+template <typename MessageType>
+void SubstraitExporter::exportAdvancedExtension(ExtensibleOpInterface op,
+                                                MessageType &message) {
+  if (!op.getAdvancedExtension())
+    return;
+
+  // Build the base `AdvancedExtension` message.
+  AdvancedExtensionAttr extensionAttr = op.getAdvancedExtension().value();
+  auto extension = std::make_unique<extensions::AdvancedExtension>();
+
+  StringAttr optimizationAttr = extensionAttr.getOptimization();
+  StringAttr enhancementAttr = extensionAttr.getEnhancement();
+
+  // Set `optimization` field if present.
+  if (optimizationAttr) {
+    std::unique_ptr<pb::Any> optimization = exportAny(optimizationAttr);
+    extension->set_allocated_optimization(optimization.release());
+  }
+
+  // Set `enhancement` field if present.
+  if (enhancementAttr) {
+    std::unique_ptr<pb::Any> enhancement = exportAny(enhancementAttr);
+    extension->set_allocated_enhancement(enhancement.release());
+  }
+
+  // Set the `advanced_extension` field in the provided message.
+  using Trait = advanced_extension_trait<MessageType>;
+  Trait::set_allocated_advanced_extension(message, extension.release());
+}
+
 std::unique_ptr<pb::Any> SubstraitExporter::exportAny(StringAttr attr) {
   auto any = std::make_unique<pb::Any>();
   auto anyType = mlir::cast<AnyType>(attr.getType());
@@ -837,26 +870,8 @@ FailureOr<std::unique_ptr<Plan>> SubstraitExporter::exportOperation(PlanOp op) {
   version->set_git_hash(op.getGitHash().str());
   plan->set_allocated_version(version.release());
 
-  // Build `AdvancedExtension` message.
-  if (op.getAdvancedExtension()) {
-    AdvancedExtensionAttr extensionAttr = op.getAdvancedExtension().value();
-    auto extension = std::make_unique<extensions::AdvancedExtension>();
-
-    StringAttr optimizationAttr = extensionAttr.getOptimization();
-    StringAttr enhancementAttr = extensionAttr.getEnhancement();
-
-    if (optimizationAttr) {
-      std::unique_ptr<pb::Any> optimization = exportAny(optimizationAttr);
-      extension->set_allocated_optimization(optimization.release());
-    }
-
-    if (enhancementAttr) {
-      std::unique_ptr<pb::Any> enhancement = exportAny(enhancementAttr);
-      extension->set_allocated_enhancement(enhancement.release());
-    }
-
-    plan->set_allocated_advanced_extensions(extension.release());
-  }
+  // Attach the `AdvancedExtension` message if the attribute exists.
+  exportAdvancedExtension(op, *plan);
 
   // Add `extension_uris` to plan.
   {
@@ -987,6 +1002,9 @@ SubstraitExporter::exportOperation(ProjectOp op) {
     *projectRel->add_expressions() = *expression.value();
   }
 
+  // Attach the `AdvancedExtension` message if the attribute exists.
+  exportAdvancedExtension(op, *projectRel);
+
   // Build `Rel` message.
   auto rel = std::make_unique<Rel>();
   rel->set_allocated_project(projectRel.release());
diff --git a/lib/Target/SubstraitPB/Import.cpp b/lib/Target/SubstraitPB/Import.cpp
index 0e4fab3d..ebb631c5 100644
--- a/lib/Target/SubstraitPB/Import.cpp
+++ b/lib/Target/SubstraitPB/Import.cpp
@@ -25,6 +25,7 @@
 
 using namespace mlir;
 using namespace mlir::substrait;
+using namespace mlir::substrait::protobuf_utils;
 using namespace ::substrait;
 using namespace ::substrait::proto;
 
@@ -64,6 +65,46 @@ DECLARE_IMPORT_FUNC(ReadRel, Rel, RelOpInterface)
 DECLARE_IMPORT_FUNC(Rel, Rel, RelOpInterface)
 DECLARE_IMPORT_FUNC(ScalarFunction, Expression::ScalarFunction, CallOp)
 
+/// If present, imports the `advanced_extension` or `advanced_extensions` field
+/// from the given message and sets the obtained attribute on the given op.
+template <typename MessageType>
+void importAdvancedExtension(ImplicitLocOpBuilder builder,
+                             ExtensibleOpInterface op,
+                             const MessageType &message);
+
+template <typename MessageType>
+void importAdvancedExtension(ImplicitLocOpBuilder builder,
+                             ExtensibleOpInterface op,
+                             const MessageType &message) {
+  using Trait = advanced_extension_trait<MessageType>;
+  if (!Trait::has_advanced_extension(message))
+    return;
+
+  // Get the `advanced_extension(s)` field.
+  const extensions::AdvancedExtension &advancedExtension =
+      Trait::advanced_extension(message);
+
+  // Import `optimization` field if present.
+  StringAttr optimizationAttr;
+  if (advancedExtension.has_optimization()) {
+    const pb::Any &optimization = advancedExtension.optimization();
+    optimizationAttr = importAny(builder, optimization).value();
+  }
+
+  // Import `enhancement` field if present.
+  StringAttr enhancementAttr;
+  if (advancedExtension.has_enhancement()) {
+    const pb::Any &enhancement = advancedExtension.enhancement();
+    enhancementAttr = importAny(builder, enhancement).value();
+  }
+
+  // Build attribute and set it on the op.
+  MLIRContext *context = builder.getContext();
+  auto advancedExtensionAttr =
+      AdvancedExtensionAttr::get(context, optimizationAttr, enhancementAttr);
+  op.setAdvancedExtensionAttr(advancedExtensionAttr);
+}
+
 FailureOr<StringAttr> importAny(ImplicitLocOpBuilder builder,
                                 const pb::Any &message) {
   MLIRContext *context = builder.getContext();
@@ -480,34 +521,15 @@ static FailureOr<PlanOp> importPlan(ImplicitLocOpBuilder builder,
   // Import version.
   const Version &version = message.version();
 
-  // Import advanced extension.
-  AdvancedExtensionAttr advancedExtensionAttr;
-  if (message.has_advanced_extensions()) {
-    const extensions::AdvancedExtension &advancedExtension =
-        message.advanced_extensions();
-
-    StringAttr optimizationAttr;
-    if (advancedExtension.has_optimization()) {
-      const pb::Any &optimization = advancedExtension.optimization();
-      optimizationAttr = importAny(builder, optimization).value();
-    }
-
-    StringAttr enhancementAttr;
-    if (advancedExtension.has_enhancement()) {
-      const pb::Any &enhancement = advancedExtension.enhancement();
-      enhancementAttr = importAny(builder, enhancement).value();
-    }
-
-    advancedExtensionAttr =
-        AdvancedExtensionAttr::get(context, optimizationAttr, enhancementAttr);
-  }
-
   // Build `PlanOp`.
   auto planOp = builder.create<PlanOp>(
       version.major_number(), version.minor_number(), version.patch_number(),
-      version.git_hash(), version.producer(), advancedExtensionAttr);
+      version.git_hash(), version.producer());
   planOp.getBody().push_back(new Block());
 
+  // Import advanced extension if it is present.
+  importAdvancedExtension(builder, planOp, message);
+
   OpBuilder::InsertionGuard insertGuard(builder);
   builder.setInsertionPointToEnd(&planOp.getBody().front());
 
@@ -668,6 +690,9 @@ static mlir::FailureOr<ProjectOp> importProjectRel(ImplicitLocOpBuilder builder,
       builder.create<ProjectOp>(resultType, inputOp.value()->getResult(0));
   projectOp.getExpressions().push_back(conditionBlock.release());
 
+  // Import advanced extension if it is present.
+  importAdvancedExtension(builder, projectOp, projectRel);
+
   return projectOp;
 }
 
diff --git a/lib/Target/SubstraitPB/ProtobufUtils.h b/lib/Target/SubstraitPB/ProtobufUtils.h
index 426d0c8e..4ea76a34 100644
--- a/lib/Target/SubstraitPB/ProtobufUtils.h
+++ b/lib/Target/SubstraitPB/ProtobufUtils.h
@@ -9,6 +9,8 @@
 #ifndef LIB_TARGET_SUBSTRAITPB_PROTOBUFUTILS_H
 #define LIB_TARGET_SUBSTRAITPB_PROTOBUFUTILS_H
 
+#include <type_traits>
+
 #include "mlir/IR/Location.h"
 
 namespace substrait::proto {
@@ -28,6 +30,59 @@ getCommon(const ::substrait::proto::Rel &rel, Location loc);
 FailureOr<::substrait::proto::RelCommon *>
 getMutableCommon(::substrait::proto::Rel *rel, Location loc);
 
+/// SFINAE-based template that checks if the given (message) type has an field
+/// called `advanced_extension`: the `value` member is `true` iff it has. This
+/// is useful to deal with the two different names, `advanced_extension` and
+/// `advanced_extensions`, that are used for the same thing across different
+/// message types in the Substrait spec.
+template <typename T>
+class has_advanced_extensions {
+  template <typename C>
+  static std::true_type test(decltype(&C::advanced_extensions));
+  template <typename C>
+  static std::false_type test(...);
+
+public:
+  static constexpr bool value = decltype(test<T>(0))::value;
+};
+
+/// Trait class for accessing the `advanced_extension` field. The default
+/// instances is automatically used for message types that call this field
+/// `advanced_extension`; the specialization below is automatically used for
+/// message types that call it `advanced_extensions`.
+template <typename T, typename = void>
+struct advanced_extension_trait {
+  static auto has_advanced_extension(const T &message) {
+    return message.has_advanced_extension();
+  }
+  static auto advanced_extension(const T &message) {
+    return message.advanced_extension();
+  }
+  template <typename S>
+  static auto set_allocated_advanced_extension(T &message,
+                                               S &&advanced_extensions) {
+    message.set_allocated_advanced_extension(
+        std::forward<S>(advanced_extensions));
+  }
+};
+
+template <typename T>
+struct advanced_extension_trait<
+    T, std::enable_if_t<has_advanced_extensions<T>::value>> {
+  static auto has_advanced_extension(const T &message) {
+    return message.has_advanced_extensions();
+  }
+  static auto advanced_extension(const T &message) {
+    return message.advanced_extensions();
+  }
+  template <typename S>
+  static auto set_allocated_advanced_extension(T &message,
+                                               S &&advanced_extensions) {
+    message.set_allocated_advanced_extensions(
+        std::forward<S>(advanced_extensions));
+  }
+};
+
 } // namespace mlir::substrait::protobuf_utils
 
 #endif // LIB_TARGET_SUBSTRAITPB_PROTOBUFUTILS_H
diff --git a/test/Dialect/Substrait/project.mlir b/test/Dialect/Substrait/project.mlir
index e5918f53..d537aba5 100644
--- a/test/Dialect/Substrait/project.mlir
+++ b/test/Dialect/Substrait/project.mlir
@@ -27,7 +27,7 @@ substrait.plan version 0 : 42 : 1 {
 
 // -----
 
-// CHECK:      substrait.plan version 0 : 42 : 1 {
+// CHECK:      substrait.plan
 // CHECK-NEXT:   relation
 // CHECK:         %[[V0:.*]] = named_table
 // CHECK-NEXT:    %[[V1:.*]] = project %[[V0]] : tuple<si32> -> tuple<si32> {
@@ -44,3 +44,25 @@ substrait.plan version 0 : 42 : 1 {
     yield %1 : tuple<si32>
   }
 }
+
+// -----
+
+// CHECK:      substrait.plan version
+// CHECK-NEXT:   relation
+// CHECK:         %[[V0:.*]] = named_table
+// CHECK-NEXT:    %[[V1:.*]] = project %[[V0]]
+// CHECK-SAME:      advanced_extension optimization = "foo" : !substrait.any<"bar">
+// CHECK-SAME:      tuple<si32> -> tuple<si32> {
+
+substrait.plan version 0 : 42 : 1 {
+  relation {
+    %0 = named_table @t1 as ["a"] : tuple<si32>
+    %1 = project %0
+            advanced_extension optimization = "foo" : !substrait.any<"bar">
+            : tuple<si32> -> tuple<si32> {
+    ^bb0(%arg0: tuple<si32>):
+      yield
+    }
+    yield %1 : tuple<si32>
+  }
+}
diff --git a/test/Target/SubstraitPB/Export/project.mlir b/test/Target/SubstraitPB/Export/project.mlir
index ca1be2df..ee33d55e 100644
--- a/test/Target/SubstraitPB/Export/project.mlir
+++ b/test/Target/SubstraitPB/Export/project.mlir
@@ -1,9 +1,12 @@
-// RUN: substrait-translate -substrait-to-protobuf %s \
+// RUN: substrait-translate -substrait-to-protobuf --split-input-file %s \
 // RUN: | FileCheck %s
 
 // RUN: substrait-translate -substrait-to-protobuf %s \
+// RUN:   --split-input-file --output-split-marker="# -----" \
 // RUN: | substrait-translate -protobuf-to-substrait \
+// RUN:   --split-input-file="# -----" --output-split-marker="// ""-----" \
 // RUN: | substrait-translate -substrait-to-protobuf \
+// RUN:   --split-input-file --output-split-marker="# -----" \
 // RUN: | FileCheck %s
 
 // CHECK-LABEL: relations {
@@ -36,3 +39,30 @@ substrait.plan version 0 : 42 : 1 {
     yield %1 : tuple<si32, si1, si32>
   }
 }
+
+// -----
+
+// CHECK-LABEL: relations {
+// CHECK-NEXT:    rel {
+// CHECK-NEXT:      project {
+// CHECK-NEXT:        common {
+// CHECK:             input {
+// CHECK:             advanced_extension {
+// CHECK-NEXT:        optimization {
+// CHECK-NEXT:          type_url: "bar"
+// CHECK-NEXT:          value: "foo"
+// CHECK-NEXT:        }
+// CHECK-NEXT:      }
+
+substrait.plan version 0 : 42 : 1 {
+  relation {
+    %0 = named_table @t1 as ["a"] : tuple<si32>
+    %1 = project %0
+            advanced_extension optimization = "foo" : !substrait.any<"bar">
+            : tuple<si32> -> tuple<si32> {
+    ^bb0(%arg0: tuple<si32>):
+      yield
+    }
+    yield %1 : tuple<si32>
+  }
+}
diff --git a/test/Target/SubstraitPB/Import/project.textpb b/test/Target/SubstraitPB/Import/project.textpb
index e22072b6..d054f3c5 100644
--- a/test/Target/SubstraitPB/Import/project.textpb
+++ b/test/Target/SubstraitPB/Import/project.textpb
@@ -1,9 +1,13 @@
 # RUN: substrait-translate -protobuf-to-substrait %s \
+# RUN:   --split-input-file="# ""-----" \
 # RUN: | FileCheck %s
 
 # RUN: substrait-translate -protobuf-to-substrait %s \
+# RUN:   --split-input-file="# ""-----" --output-split-marker="// -----" \
 # RUN: | substrait-translate -substrait-to-protobuf \
+# RUN:   --split-input-file --output-split-marker="# ""-----" \
 # RUN: | substrait-translate -protobuf-to-substrait \
+# RUN:   --split-input-file="# ""-----" --output-split-marker="// -----" \
 # RUN: | FileCheck %s
 
 # CHECK:      substrait.plan version 0 : 42 : 1 {
@@ -63,3 +67,54 @@ version {
   minor_number: 42
   patch_number: 1
 }
+
+# -----
+
+# CHECK:      substrait.plan version
+# CHECK-NEXT:   relation
+# CHECK:         %[[V0:.*]] = named_table
+# CHECK-NEXT:    %[[V1:.*]] = project %[[V0]]
+# CHECK-SAME:      advanced_extension optimization = "foo" : !substrait.any<"bar">
+
+relations {
+  rel {
+    project {
+      common {
+        direct {
+        }
+      }
+      input {
+        read {
+          common {
+            direct {
+            }
+          }
+          base_schema {
+            names: "a"
+            struct {
+              types {
+                i32 {
+                  nullability: NULLABILITY_REQUIRED
+                }
+              }
+              nullability: NULLABILITY_REQUIRED
+            }
+          }
+          named_table {
+            names: "t1"
+          }
+        }
+      }
+      advanced_extension {
+        optimization {
+          type_url: "bar"
+          value: "foo"
+        }
+      }
+    }
+  }
+}
+version {
+  minor_number: 42
+  patch_number: 1
+}