diff --git a/src/ast.rs b/src/ast.rs
index 1dc9ab9..d2020a8 100644
--- a/src/ast.rs
+++ b/src/ast.rs
@@ -1,3 +1,6 @@
+//! Represents the WIT language as a tree. This is the central
+//! representation of the language.
+
 use crate::interpreter::Instruction;
 use std::str;
 
diff --git a/src/decoders/mod.rs b/src/decoders/mod.rs
index 96eab66..0ac9d88 100644
--- a/src/decoders/mod.rs
+++ b/src/decoders/mod.rs
@@ -1 +1,4 @@
+//! Reads the AST from a particular data representation; for instance,
+//! `decoders::binary` reads the AST from a binary.
+
 pub mod binary;
diff --git a/src/encoders/mod.rs b/src/encoders/mod.rs
index 070bf58..ae1611e 100644
--- a/src/encoders/mod.rs
+++ b/src/encoders/mod.rs
@@ -1 +1,5 @@
+//! Writes the AST into a particular format; for instance,
+//! `encoders::wat` writes the AST into a string representing WIT with
+//! its textual format.
+
 pub mod wat;
diff --git a/src/interpreter/mod.rs b/src/interpreter/mod.rs
index 551311a..d9452ab 100644
--- a/src/interpreter/mod.rs
+++ b/src/interpreter/mod.rs
@@ -1,3 +1,5 @@
+//! A stack-based interpreter to execute instructions of WIT adapters.
+
 mod instruction;
 mod instructions;
 pub mod stack;