diff --git a/CHANGELOG.md b/CHANGELOG.md
index cdd2b76..14d2fa6 100644
--- a/CHANGELOG.md
+++ b/CHANGELOG.md
@@ -146,7 +146,7 @@ and this project adheres to [Semantic Versioning](https://semver.org/spec/v2.0.0
 
 ### Added
 
- - `ML99_assignInitializerList(Stmt)` as `ML99_assign(Stmt)` counterparts for initialiser lists.
+ - `ML99_assignInitializerList(Stmt)` as `ML99_assign(Stmt)` counterparts for initializer lists.
 
 ## 1.4.1 - 2021-08-05
 
@@ -255,7 +255,7 @@ and this project adheres to [Semantic Versioning](https://semver.org/spec/v2.0.0
 ### Fixed
 
  - `assert.h`:
-   - Parenthesise expressions passed to `ML99_ASSERT`, `ML99_ASSERT_EQ`.
+   - Parenthesize expressions passed to `ML99_ASSERT`, `ML99_ASSERT_EQ`.
 
 ### Changed
 
@@ -371,7 +371,7 @@ and this project adheres to [Semantic Versioning](https://semver.org/spec/v2.0.0
 
 ### Fixed
 
- - Initialise variables produced by `M_semicolon` and `M_assertPlain` to suppress warnings.
+ - Initialize variables produced by `M_semicolon` and `M_assertPlain` to suppress warnings.
 
 ## 0.4.0 - 2021-02-26
 
diff --git a/README.md b/README.md
index 8b40997..7c0b17e 100644
--- a/README.md
+++ b/README.md
@@ -268,7 +268,7 @@ See [`ARCHITECTURE.md`](ARCHITECTURE.md).
 
 See [`idioms.md`](idioms.md).
 
-## Optimisation tips
+## Optimization tips
 
 See [`optimization_tips.md`](optimization_tips.md).
 
diff --git a/include/metalang99/eval/eval.h b/include/metalang99/eval/eval.h
index ce2ca0a..ebf83f5 100644
--- a/include/metalang99/eval/eval.h
+++ b/include/metalang99/eval/eval.h
@@ -97,7 +97,7 @@
         ~)
 
 /*
- * In this subroutine, we employ the following optimisation:
+ * In this subroutine, we employ the following optimization:
  *
  *  - If `evaluated_op` expands to many terms, we first evaluate these terms and accumulate them
  * (`ML99_PRIV_EVAL_0callUneval_K_1`).
diff --git a/include/metalang99/lang.h b/include/metalang99/lang.h
index 45ded6c..299f8d7 100644
--- a/include/metalang99/lang.h
+++ b/include/metalang99/lang.h
@@ -191,7 +191,7 @@
 #define ML99_abort(...) (0abort, __VA_ARGS__)
 
 /**
- * A convenience macro to emphasise that your metafunction expands to more than one term.
+ * A convenience macro to emphasize that your metafunction expands to more than one term.
  *
  * This macro just expands to provided arguments.
  *
diff --git a/include/metalang99/stmt.h b/include/metalang99/stmt.h
index d2bf74b..87c4b6b 100644
--- a/include/metalang99/stmt.h
+++ b/include/metalang99/stmt.h
@@ -60,7 +60,7 @@
  * The same as #ML99_INTRODUCE_VAR_TO_STMT but deals with a single non-`NULL` pointer.
  *
  * In comparison with #ML99_INTRODUCE_VAR_TO_STMT, this macro generates a little less code. It
- * introduces a pointer to @p ty identified by @p name and initialised to @p init.
+ * introduces a pointer to @p ty identified by @p name and initialized to @p init.
  *
  * Top-level `break`/`continue` inside a user-provided statement are prohibited.
  *
diff --git a/optimization_tips.md b/optimization_tips.md
index 90bf27a..261cbe8 100644
--- a/optimization_tips.md
+++ b/optimization_tips.md
@@ -1,6 +1,6 @@
 # Optimization tips
 
-_This document describes a few optimisation tips when using Metalang99._
+_This document describes a few optimization tips when using Metalang99._
 
 Generally speaking, the fewer reduction steps you perform, the faster you become. A reduction step is a concept defined formally by the [specification]. Here is its informal (and imprecise) description:
 
@@ -11,7 +11,7 @@ To perform fewer reduction steps, you can:
 
  - use `ML99_callUneval`,
  - use plain macros (e.g., `ML99_CAT` instead of `ML99_cat`),
- - use optimised versions (e.g., `ML99_listMapInPlace`),
+ - use optimized versions (e.g., `ML99_listMapInPlace`),
  - use tuples/variadics instead of lists,
  - call a macro as `<X>_IMPL(...)`, if all the arguments are already evaluated.