diff --git a/Network/Wai.hs b/Network/Wai.hs
--- a/Network/Wai.hs
+++ b/Network/Wai.hs
@@ -5,7 +5,7 @@
 This module defines a generic web application interface. It is a common
 protocol between web servers and web applications.
 
-The overriding design principles here are performance and generality . To
+The overriding design principles here are performance and generality. To
 address performance, this library is built on top of the conduit and
 blaze-builder packages.  The advantages of conduits over lazy IO have been
 debated elsewhere and so will not be addressed here.  However, helper functions
@@ -36,7 +36,7 @@
 -}
 module Network.Wai
     (
-      -- * Ttypes
+      -- * Types
       Application
     , Middleware
       -- * Request
@@ -69,6 +69,7 @@
     , responseLBS
     , responseSource
     , responseSourceBracket
+    , responseRaw
       -- * Response accessors
     , responseStatus
     , responseHeaders
@@ -153,6 +154,22 @@
         return $ ResponseSource st hdr $ \f ->
             bracket (return resource) teardown (\_ -> f src)
 
+-- | Create a response for a raw application. This is useful for \"upgrade\"
+-- situations such as WebSockets, where an application requests for the server
+-- to grant it raw network access.
+--
+-- This function requires a backup response to be provided, for the case where
+-- the handler in question does not support such upgrading (e.g., CGI apps).
+--
+-- In the event that you read from the request body before returning a
+-- @responseRaw@, behavior is undefined.
+--
+-- Since 2.1.0
+responseRaw :: (C.Source IO B.ByteString -> C.Sink B.ByteString IO () -> IO ())
+            -> Response
+            -> Response
+responseRaw rawApp fallback = ResponseRaw ($ rawApp) fallback
+
 ----------------------------------------------------------------
 
 -- | Accessing 'H.Status' in 'Response'.
@@ -160,12 +177,14 @@
 responseStatus (ResponseFile    s _ _ _) = s
 responseStatus (ResponseBuilder s _ _  ) = s
 responseStatus (ResponseSource  s _ _  ) = s
+responseStatus (ResponseRaw _ res      ) = responseStatus res
 
 -- | Accessing 'H.Status' in 'Response'.
 responseHeaders :: Response -> H.ResponseHeaders
 responseHeaders (ResponseFile    _ hs _ _) = hs
 responseHeaders (ResponseBuilder _ hs _  ) = hs
 responseHeaders (ResponseSource  _ hs _  ) = hs
+responseHeaders (ResponseRaw _ res)        = responseHeaders res
 
 -- | Converting the body information in 'Response' to 'Source'.
 responseToSource :: Response
@@ -177,6 +196,7 @@
     (s, h, \f -> IO.withFile fp IO.ReadMode $ \handle -> f $ CB.sourceHandle handle C.$= CL.map (C.Chunk . fromByteString))
 responseToSource (ResponseBuilder s h b) =
     (s, h, ($ CL.sourceList [C.Chunk b]))
+responseToSource (ResponseRaw _ res) = responseToSource res
 
 sourceFilePart :: IO.Handle -> FilePart -> C.Source IO B.ByteString
 sourceFilePart handle (FilePart offset count _) =
@@ -194,7 +214,7 @@
 --
 -- 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 signatures for this middleware
+-- string map \[(String, String)\]. A logical type signature for this middleware
 -- might be:
 --
 -- @ loadSession :: ([(String, String)] -> Application) -> Application @
diff --git a/Network/Wai/Internal.hs b/Network/Wai/Internal.hs
--- a/Network/Wai/Internal.hs
+++ b/Network/Wai/Internal.hs
@@ -11,11 +11,7 @@
 import qualified Data.Conduit                 as C
 import           Data.Text                    (Text)
 import           Data.Typeable                (Typeable)
-#if MIN_VERSION_vault(0,3,0)
 import Data.Vault.Lazy (Vault)
-#else
-import Data.Vault (Vault)
-#endif
 import           Data.Word                    (Word64)
 import qualified Network.HTTP.Types           as H
 import           Network.Socket               (SockAddr)
@@ -87,7 +83,11 @@
     = ResponseFile H.Status H.ResponseHeaders FilePath (Maybe FilePart)
     | ResponseBuilder H.Status H.ResponseHeaders Builder
     | ResponseSource H.Status H.ResponseHeaders (forall b. WithSource IO (C.Flush Builder) b)
+    | ResponseRaw (forall b. WithRawApp b) Response
   deriving Typeable
+
+type RawApp = C.Source IO B.ByteString -> C.Sink B.ByteString IO () -> IO ()
+type WithRawApp b = (RawApp -> IO b) -> IO b
 
 -- | Auxiliary type for 'ResponseSource'.
 type WithSource m a b = (C.Source m a -> m b) -> m b
diff --git a/wai.cabal b/wai.cabal
--- a/wai.cabal
+++ b/wai.cabal
@@ -1,5 +1,5 @@
 Name:                wai
-Version:             2.0.0
+Version:             2.1.0
 Synopsis:            Web Application Interface.
 Description:         Provides a common protocol for communication between web applications and web servers.
 License:             MIT
@@ -25,7 +25,7 @@
                    , http-types                >= 0.7
                    , text                      >= 0.7
                    , transformers              >= 0.2.2
-                   , vault                     >= 0.1      && < 0.4
+                   , vault                     >= 0.3      && < 0.4
   Exposed-modules:   Network.Wai
                      Network.Wai.Internal
   ghc-options:       -Wall