diff --git a/lang/func.c b/lang/func.c
index 82bfd32..395d51e 100644
--- a/lang/func.c
+++ b/lang/func.c
@@ -21,6 +21,7 @@
 	(void)obj;
 	int arg_count = vm_stack_depth(state);
 	abort_if(arg_count != 1, "func_add called with more than 1 argument");
+	// For now just call bytecode_run
 	bytecode_run(state);
 }
 
diff --git a/lang/object.h b/lang/object.h
index e42008b..dfb04df 100644
--- a/lang/object.h
+++ b/lang/object.h
@@ -19,9 +19,13 @@
 		*calls; // Points to array terminated by call with NULL name
 };
 
+// Creates an object with a class and allocated private data
 Object object_create(struct object_class *class, int priv_size);
+
+// Retrieves private data for an object with a specified class
 char *object_priv(Object object, struct object_class *class);
 
+// Creates a placeholder object for use when no object is present
 Object object_none(void);
 
 // Adds a reference to an object
diff --git a/lang/types.h b/lang/types.h
index 1dfebae..2e7668b 100644
--- a/lang/types.h
+++ b/lang/types.h
@@ -4,7 +4,10 @@
 #ifndef TYPES_H
 #define TYPES_H
 
+// Opaque type for an object
 typedef void *Object;
+
+// Opaque type for the VM state
 typedef void *VmState;
 
 #endif
diff --git a/lang/vm.h b/lang/vm.h
index 76c8914..052c7d4 100644
--- a/lang/vm.h
+++ b/lang/vm.h
@@ -6,16 +6,37 @@
 
 #include "types.h"
 
+// Creates a virtual machine
 VmState vm_create(void);
+
+// Destroys a virtual machine
 void vm_destroy(VmState *state);
 
+// Sets the value of a vm stack element
+// index is relative to the current frame
+// The object's reference is taken from the caller
 void vm_stack_set(VmState state, int index, Object obj);
+
+// Gets the value of a vm stack element
+// index is relative to the current frame
+// A new reference is created for the caller
 Object vm_stack_get(VmState state, int index);
+
+// Pushes an object to the top of the vm stack
+// The object's reference is taken from the caller
 void vm_stack_push(VmState state, Object obj);
+
+// Pops a object from the top of the vm stack
+// The object's reference is given to the caller
 Object vm_stack_pop(VmState state);
+
+// Drops a number of objects from the vm stack
 void vm_stack_drop(VmState state, int count);
+
+// Gets the depth of the current vm stack frame
 int vm_stack_depth(VmState state);
 
+// Creates a stack frame at arg_count offset from the top then calls an object
 void vm_call(VmState state, Object obj, const char *name, int arg_count);
 
 #endif