diff --git a/os-big-bang.rkt b/os-big-bang.rkt
index e8603d4..39e87c1 100644
--- a/os-big-bang.rkt
+++ b/os-big-bang.rkt
@@ -69,6 +69,10 @@
 ;; representation of a suspended world and its active subscriptions.
 (struct world (state subscriptions) #:transparent)
 
+;; (subscribe/fresh var expr)
+;; Generates a fresh SID, binds it to var, and results in a
+;; subscription using that SID with the given expr's
+;; event-description.
 (define-syntax subscribe/fresh
   (syntax-rules ()
     ((_ id-binder event-description)
@@ -84,16 +88,26 @@
 			   (match message
 			     [pattern body ...] ...))))))
 
+;; (message-handlers state-pat [pat expr ...] ...)
+;; When one of these message handlers is invoked, binds the
+;; world-state value active at the time using state-pat, binds the
+;; message using pat, and then invokes the exprs. The pat serves
+;; double-duty: it both destructures the message and acts as a
+;; predicate controlling receipt of the message.
 (define-syntax message-handlers
   (syntax-rules ()
     ((_ old-state-pattern [pattern body ...] ...)
      (message-handlers* on-message old-state-pattern [pattern body ...] ...))))
 
+;; As for message-handlers, but builds a meta-message handling
+;; event-description instead.
 (define-syntax meta-message-handlers
   (syntax-rules ()
     ((_ old-state-pattern [pattern body ...] ...)
      (message-handlers* on-meta-message old-state-pattern [pattern body ...] ...))))
 
+;; Complex form for writing meta-message handlers at ground level,
+;; which translate to event handlers. See examples in various drivers.
 (define-syntax ground-message-handler
   (syntax-rules (=>)
     ((_ old-state-pattern [(tag-expr evt-expr => pattern) body ...])
@@ -103,6 +117,9 @@
 			(match meta-message
 			  [(ground-event-value _ pattern) body ...]))))))
 
+;; World -> Suspension
+;; Used to package up our persistent subscriptions into a transient
+;; os.rkt Suspension.
 (define (world->os-suspension w)
   (suspension w
 	      #f
@@ -117,14 +134,17 @@
 		(match-define (on-meta-message pattern handler) v)
 		(message-handler pattern (wrap-handler handler)))))
 
+;; (X WorldState -> Transition) -> X -> WorldState -> Transition
 (define (((wrap-handler handler) message) w)
   (maybe-transition->os-transition w (handler message (world-state w))))
 
+;; World Transition -> KernelModeTransition
 (define (maybe-transition->os-transition w t)
   (if (transition? t)
       (transition->os-transition w t)
       (transition->os-transition w (transition t '()))))
 
+;; World (transition WorldState ListOf<Action>) -> KernelModeTransition
 (define (transition->os-transition w t)
   (match-define (transition state unflattened-actions) t)
   (define actions (flatten unflattened-actions))
@@ -136,6 +156,9 @@
 			  (for/list [(a actions) #:when (spawn? a)]
 			    (spawn-thunk a))))
 
+;; World WorldState ListOf<Action> -> World
+;; Updates the World according to the given Actions, and also replaces
+;; the old with the new WorldState in the result.
 (define (update-world w new-state actions)
   (world new-state
 	 (foldl (lambda (action old-map)
@@ -150,8 +173,10 @@
 		(world-subscriptions w)
 		actions)))
 
+;; WorldState [Action ...] -> BootK
 (define (os-big-bang initial-state . initial-actions)
   (os-big-bang/transition (transition initial-state initial-actions)))
 
+;; (transition WorldState ListOf<Action>) -> BootK
 (define (os-big-bang/transition t)
   (lambda () (transition->os-transition (world (void) (hash)) t)))
diff --git a/os-userland-stdlib.rkt b/os-userland-stdlib.rkt
index e815424..fd21b39 100644
--- a/os-userland-stdlib.rkt
+++ b/os-userland-stdlib.rkt
@@ -1,4 +1,5 @@
 #lang racket/base
+;; Some basic drivers and utilities for writing programs using os-userland.rkt
 
 (require racket/match)
 (require racket/port)
@@ -29,9 +30,17 @@
 	 receive
 	 receive/timeout)
 
+;; BootK -> Void
+;; Starts the ground VM with the given BootK and a PatternPredicate
+;; appropriate for use with this library.
 (define (ground-vm/stdlib boot)
   (ground-vm boot #:pattern-predicate (lambda (p m) (p m))))
 
+;; (message-handlers [pat expr ...] ...)
+;; When one of these message handlers is invoked, binds the message
+;; using pat, and then invokes the exprs. The pat serves double-duty:
+;; it both destructures the message and acts as a predicate
+;; controlling receipt of the message.
 (define-syntax message-handlers
   (syntax-rules ()
     ((_ (pattern body ...) ...)
@@ -39,6 +48,8 @@
 			(match-lambda (pattern body ...)))
 	   ...))))
 
+;; For matching *ground* events. See also ground-message-handler in
+;; os-big-bang.rkt.
 (define-syntax meta-message-handlers
   (syntax-rules (=>)
     ((_ [(tag-expr evt-expr => pattern) body ...] ...)
@@ -46,6 +57,8 @@
 			(match-lambda ((ground-event-value _ pattern) body ...)))
 	   ...))))
 
+;; Any -> Any
+;; Performs an RPC, according to a simple stereotypical RPC protocol.
 (define (rpc req)
   (define reply-addr (gensym 'reply-addr)) ;;; !!! TODO: remove side-effect?
   (send `(request ,reply-addr ,req))
@@ -53,6 +66,10 @@
 	 [`(reply ,(== reply-addr) ,v)
 	  v])))
 
+;; (rpc-service (pat expr ...) ...)
+;; Starts an RPC service listening for messages matching the
+;; pats. When one arrives, spawns a new process that runs the
+;; corresponding exprs, and goes back to listening for more requests.
 (define-syntax rpc-service
   (syntax-rules ()
     [(_ [pattern body ...] ...)
@@ -65,6 +82,7 @@
 	      ...))
        (loop))]))
 
+;; Driver wrapping output to current-output-port.
 (define display-driver
   (userland
    (lambda ()
@@ -75,9 +93,11 @@
 		    (flush-output)))
        (loop)))))
 
+;; Sends its argument to the display-driver.
 (define (display x)
   (send `(display ,x)))
 
+;; Driver providing an RPC read-line (from current-input-port) service.
 (define read-line-driver
   (userland
    (lambda ()
@@ -89,9 +109,11 @@
 			   => line)
 			  line]))]))))
 
+;; Requests the next line of input.
 (define (read-line)
   (rpc 'read-line))
 
+;; Racket timer event - see comment on the analogous function in os-timer.rkt.
 (define (time-evt msecs)
   (wrap-evt (alarm-evt msecs) (lambda (_) (current-inexact-milliseconds))))
 
@@ -106,9 +128,12 @@
   (wait (message-handlers)
 	(wait-mmh msecs)))
 
+;; Retrieves the current-inexact-milliseconds, using the VM tree IPC mechanism.
 (define (current-time)
   (wait-until-time 0))
 
+;; RPC service that replies to you when the specified number of
+;; milliseconds have elapsed.
 (define sleep-driver
   (userland
    (lambda ()
@@ -119,14 +144,18 @@
        (send `(display "\n"))
        now]))))
 
+;; Invoke the sleep-driver.
 (define (sleep msecs)
   (rpc `(sleep ,msecs)))
 
+;; Syntactic sugar for a (wait (message-handlers ...)) combination.
 (define-syntax receive
   (syntax-rules ()
     ((_ mh-clause ...)
      (wait (message-handlers mh-clause ...)))))
 
+;; Syntactic sugar for a (wait (message-handlers ...)) combination
+;; with an additional timeout event.
 (define-syntax receive/timeout
   (syntax-rules ()
     ((_ timeout-msecs mh-clause ...)
diff --git a/os-userland.rkt b/os-userland.rkt
index 2a292ef..a963205 100644
--- a/os-userland.rkt
+++ b/os-userland.rkt
@@ -1,5 +1,4 @@
 #lang racket/base
-
 ; Userland for os.rkt: use of delimited continuations to invoke kernel services
 
 (require racket/match)
@@ -23,8 +22,12 @@
 
 	 spawn)
 
+;; A WaitClause is a (wait-clause PatternPredicate ([Meta]Message -> Any))
+;; Used to build up what amount to wrapped events in Racket's CMLish
+;; terminology, for use with wait (which is analogous to sync).
 (struct wait-clause (pattern handler-proc) #:transparent)
 
+;; Our internal prompt tag.
 (define prompt (make-continuation-prompt-tag 'os-userland))
 
 ;; ( -> Void) -> BootK
@@ -81,20 +84,33 @@
 (define (actions ms mms thrs)
   (call-in-kernel-context (lambda (k) `(actions ,ms ,mms ,thrs ,k))))
 
+;; Message -> Void
+;; Sends a message at this level.
 (define (send message)
   (actions (list message) '() '()))
 
+;; MetaMessage -> Void
+;; Sends a message at this VM's container's level.
 (define (meta-send meta-message)
   (actions '() (list meta-message) '()))
 
+;; ListOf<Message> [ListOf<MetaMessage>] -> Void
+;; Sends any number of messages, possibly at multiple levels.
 (define (send* messages [meta-messages '()])
   (actions messages meta-messages '()))
 
+;; ConsTreeOf<WaitClause> [ConsTreeOf<WaitClause>] -> Any
+;; Synchronizes on a collection of possible events.
 (define (wait mhs [mmhs '()])
   (call-in-kernel-context (lambda (k) `(wait #f ,mhs ,mmhs ,k))))
 
+;; [ConsTreeOf<WaitClause>] [ConsTreeOf<WaitClause>] -> Any
+;; Synchronizes on a collection of possible events, returning
+;; "immediately" if none of them are ready to fire.
 (define (poll [mhs '()] [mmhs '()])
   (call-in-kernel-context (lambda (k) `(wait #t ,mhs ,mmhs ,k))))
 
+;; BootK -> Void
+;; Spawns the given BootK within the current VM.
 (define (spawn thunk)
   (actions '() '() (list thunk)))
diff --git a/universe.rkt b/universe.rkt
index b44d3cf..871b69a 100644
--- a/universe.rkt
+++ b/universe.rkt
@@ -1,5 +1,4 @@
 #lang racket/base
-
 ;; Compatibility: 2htdp/universe's big-bang expressed in terms of ground-vm and os-big-bang.
 
 (require racket/match)