diff --git a/lib/heap.h b/lib/heap.h
index 0f25a5a..186eedd 100644
--- a/lib/heap.h
+++ b/lib/heap.h
@@ -20,6 +20,18 @@
 
 #define PAGE_DEFAULT_SIZE 256
 
+/**
+   @brief Some fixed portion of bytes allocated on the heap in a
+   linked list.
+
+   @details A fixed allocation of bytes, with size and a link to the
+   next page.  Cannot be resized nor can it be stack allocated the
+   usual way due to flexible array attached.
+
+   @prop[next] Next page in the linked list
+   @prop[available] Available number of bytes in page
+   @prop[data] Buffer of bytes attached to page
+ */
 typedef struct Page
 {
   struct Page *next;
@@ -27,18 +39,92 @@ typedef struct Page
   byte_t data[];
 } page_t;
 
-page_t *page_create(size_t, page_t *);
-void page_delete(page_t *);
+/**
+   @brief Allocate a new page on the heap with the given properties.
 
+   @details Allocates a new page using malloc with the given size and
+   pointer to next page.  NOTE: all memory is 0 initialised by
+   default.
+
+   @param[max] Maximum available memory in page
+   @param[next] Next page to link this page to
+ */
+page_t *page_create(size_t max, page_t *next);
+
+/**
+   @brief Delete a page, freeing its memory
+
+   @details Free's the memory associated with the page via free().
+   NOTE: any pointer's to the page's memory are considered invalid
+   once this is called.
+
+   @param[page] Page to delete
+ */
+void page_delete(page_t *page);
+
+/**
+   @brief A collection of pages through which generic allocations can
+   occur.
+
+   @details Structure which maintains a linked list of pages (with a
+   reference to the beginning and end of it).
+
+   @prop[beg] Beginning of linked list of pages
+   @prop[end] End of linked list of pages
+   @prop[pages] Number of pages allocated in heap
+ */
 typedef struct
 {
   page_t *beg, *end;
   size_t pages;
 } heap_t;
 
-void heap_create(heap_t *);
-page_t *heap_allocate(heap_t *, size_t);
-bool heap_free(heap_t *, page_t *);
+/**
+   @brief Instantiate a new heap structure
+
+   @details Initialises the heap structure given.  No heap allocation
+   occurs here until a new page is created, so this may be called
+   safely.
+
+   @param[heap] Pointer to heap to initialise
+ */
+void heap_create(heap_t *heap);
+
+/**
+   @brief Allocate a new page on the heap
+
+   @details Creates and joins a new page onto the linked list
+   maintained by the heap.  heap.end is set to this new page.
+
+   @param[heap] Heap to create a new page on
+   @param[size] Size of page to allocate
+
+   @return The newly allocated page
+ */
+page_t *heap_allocate(heap_t *heap, size_t size);
+
+/**
+   @brief Free a page of memory from the heap
+
+   @details The page given is removed from the linked list of pages
+   then freed from the heap via page_delete().  If the page does not
+   belong to this heap (O(heap.pages) time) then false is returned,
+   otherwise true.
+
+   @param[heap] Heap to free page from
+   @param[page] Page to delete
+
+   @return Success of deletion
+ */
+bool heap_free(heap_t *heap, page_t *page);
+
+/**
+   @brief Stop the heap, freeing all associated memory
+
+   @details Traverses the linked list of pages, deleting each one.
+
+   @param[heap] Heap to stop
+ */
 void heap_stop(heap_t *);
 
 #endif
diff --git a/todo.org b/todo.org
index 7c564b2..c4d07d4 100644
--- a/todo.org
+++ b/todo.org
@@ -5,10 +5,10 @@
 
 * TODO Better documentation [0%] :DOC:
 ** TODO Comment coverage [0%]
-*** WIP Lib [50%]
+*** WIP Lib [75%]
 **** DONE lib/base.h
 **** DONE lib/darr.h
-**** TODO lib/heap.h
+**** DONE lib/heap.h
 **** TODO lib/inst.h
 *** TODO VM [0%]
 **** TODO vm/runtime.h