diff --git a/Network/Wai.hs b/Network/Wai.hs
--- a/Network/Wai.hs
+++ b/Network/Wai.hs
@@ -71,10 +71,15 @@
     , responseLBS
     , responseStream
     , responseRaw
-      -- * Response accessors
+      -- ** Response accessors
     , responseStatus
     , responseHeaders
+      -- ** Response modifiers
     , responseToStream
+    , mapResponseHeaders
+      -- * Middleware composition
+    , ifRequest
+    , modifyResponse
     ) where
 
 import           Blaze.ByteString.Builder     (Builder, fromLazyByteString)
@@ -225,6 +230,13 @@
     (s, h, \withBody -> withBody $ \sendChunk _flush -> sendChunk b)
 responseToStream (ResponseRaw _ res) = responseToStream res
 
+-- | Apply the provided function to the response header list of the Response.
+mapResponseHeaders :: (H.ResponseHeaders -> H.ResponseHeaders) -> Response -> Response
+mapResponseHeaders f (ResponseFile s h b1 b2) = ResponseFile s (f h) b1 b2
+mapResponseHeaders f (ResponseBuilder s h b) = ResponseBuilder s (f h) b
+mapResponseHeaders f (ResponseStream s h b) = ResponseStream s (f h) b
+mapResponseHeaders _ r@(ResponseRaw _ _) = r
+
 ----------------------------------------------------------------
 
 -- | The WAI application.
@@ -242,21 +254,6 @@
 -- @
 type Application = Request -> (Response -> IO ResponseReceived) -> IO ResponseReceived
 
--- | Middleware is a component that sits between the server and application. It
--- can do such tasks as GZIP encoding or response caching. What follows is the
--- general definition of middleware, though a middleware author should feel
--- free to modify this.
---
--- As an example of an alternate type for middleware, suppose you write a
--- function to load up session information. The session information is simply a
--- string map \[(String, String)\]. A logical type signature for this middleware
--- might be:
---
--- @ loadSession :: ([(String, String)] -> Application) -> Application @
---
--- Here, instead of taking a standard 'Application' as its first argument, the
--- middleware takes a function which consumes the session information as well.
-type Middleware = Application -> Application
 
 -- | A default, blank request.
 --
@@ -278,6 +275,36 @@
     , requestHeaderHost = Nothing
     , requestHeaderRange = Nothing
     }
+
+
+-- | Middleware is a component that sits between the server and application. It
+-- can do such tasks as GZIP encoding or response caching. What follows is the
+-- general definition of middleware, though a middleware author should feel
+-- free to modify this.
+--
+-- As an example of an alternate type for middleware, suppose you write a
+-- function to load up session information. The session information is simply a
+-- string map \[(String, String)\]. A logical type signature for this middleware
+-- might be:
+--
+-- @ loadSession :: ([(String, String)] -> Application) -> Application @
+--
+-- Here, instead of taking a standard 'Application' as its first argument, the
+-- middleware takes a function which consumes the session information as well.
+type Middleware = Application -> Application
+
+
+-- | apply a function that modifies a response as a 'Middleware'
+modifyResponse :: (Response -> Response) -> Middleware
+modifyResponse f app req respond = app req $ respond . f
+
+
+-- | conditionally apply a 'Middleware'
+ifRequest :: (Request -> Bool) -> Middleware -> Middleware
+ifRequest rpred middle app req | rpred req = middle app req
+                               | otherwise =        app req
+
+
 
 -- | Get the request body as a lazy ByteString. However, do /not/ use any lazy
 -- I\/O, instead reading the entire body into memory strictly.
diff --git a/wai.cabal b/wai.cabal
--- a/wai.cabal
+++ b/wai.cabal
@@ -1,5 +1,5 @@
 Name:                wai
-Version:             3.0.2.3
+Version:             3.0.3.0
 Synopsis:            Web Application Interface.
 Description:         Provides a common protocol for communication between web applications and web servers.
 description:         API docs and the README are available at <http://www.stackage.org/package/wai>.