diff --git a/ChangeLog.md b/ChangeLog.md
--- a/ChangeLog.md
+++ b/ChangeLog.md
@@ -1,3 +1,7 @@
+## 1.4.21
+
+* Add support for `Encoding` from `aeson-0.11` [#1241](https://github.com/yesodweb/yesod/pull/1241)
+
 ## 1.4.20.2
 
 * GHC 8 support
diff --git a/Yesod/Core/Class/Yesod.hs b/Yesod/Core/Class/Yesod.hs
--- a/Yesod/Core/Class/Yesod.hs
+++ b/Yesod/Core/Class/Yesod.hs
@@ -226,11 +226,7 @@
     messageLoggerSource site = defaultMessageLoggerSource $ shouldLogIO site
 
     -- | Where to Load sripts from. We recommend the default value,
-    -- 'BottomOfBody'.  Alternatively use the built in async yepnope loader:
-    --
-    -- > BottomOfHeadAsync $ loadJsYepnope $ Right $ StaticR js_modernizr_js
-    --
-    -- Or write your own async js loader.
+    -- 'BottomOfBody'.
     jsLoader :: site -> ScriptLoadPosition site
     jsLoader _ = BottomOfBody
 
diff --git a/Yesod/Core/Content.hs b/Yesod/Core/Content.hs
--- a/Yesod/Core/Content.hs
+++ b/Yesod/Core/Content.hs
@@ -251,9 +251,20 @@
 #else
               . fromValue
 #endif
+
+#if MIN_VERSION_aeson(0, 11, 0)
+instance ToContent J.Encoding where
+    toContent = flip ContentBuilder Nothing . J.fromEncoding
+#endif
+
 instance HasContentType J.Value where
     getContentType _ = typeJson
 
+#if MIN_VERSION_aeson(0, 11, 0)
+instance HasContentType J.Encoding where
+    getContentType _ = typeJson
+#endif
+
 instance HasContentType Html where
     getContentType _ = typeHtml
 
@@ -289,6 +300,10 @@
     toTypedContent (RepXml c) = TypedContent typeXml c
 instance ToTypedContent J.Value where
     toTypedContent v = TypedContent typeJson (toContent v)
+#if MIN_VERSION_aeson(0, 11, 0)
+instance ToTypedContent J.Encoding where
+    toTypedContent e = TypedContent typeJson (toContent e)
+#endif
 instance ToTypedContent Html where
     toTypedContent h = TypedContent typeHtml (toContent h)
 instance ToTypedContent T.Text where
diff --git a/Yesod/Core/Json.hs b/Yesod/Core/Json.hs
--- a/Yesod/Core/Json.hs
+++ b/Yesod/Core/Json.hs
@@ -6,6 +6,9 @@
       defaultLayoutJson
     , jsonToRepJson
     , returnJson
+#if MIN_VERSION_aeson(0, 11, 0)
+    , returnJsonEncoding
+#endif
     , provideJson
 
       -- * Convert to a JSON value
@@ -24,6 +27,9 @@
 
       -- * Convenience functions
     , jsonOrRedirect
+#if MIN_VERSION_aeson(0, 11, 0)
+    , jsonEncodingOrRedirect
+#endif
     , acceptsJson
     ) where
 
@@ -52,35 +58,51 @@
 -- data, using the default layout for the HTML output
 -- ('defaultLayout').
 --
--- /Since: 0.3.0/
+-- @since 0.3.0
 defaultLayoutJson :: (Yesod site, J.ToJSON a)
                   => WidgetT site IO ()  -- ^ HTML
                   -> HandlerT site IO a  -- ^ JSON
                   -> HandlerT site IO TypedContent
 defaultLayoutJson w json = selectRep $ do
     provideRep $ defaultLayout w
+#if MIN_VERSION_aeson(0, 11, 0)
+    provideRep $ fmap J.toEncoding json
+#else
     provideRep $ fmap J.toJSON json
+#endif
 
 -- | Wraps a data type in a 'RepJson'.  The data type must
 -- support conversion to JSON via 'J.ToJSON'.
 --
--- /Since: 0.3.0/
+-- @since 0.3.0
 jsonToRepJson :: (Monad m, J.ToJSON a) => a -> m J.Value
 jsonToRepJson = return . J.toJSON
 {-# DEPRECATED jsonToRepJson "Use returnJson instead" #-}
 
 -- | Convert a value to a JSON representation via aeson\'s 'J.toJSON' function.
 --
--- Since 1.2.1
+-- @since 1.2.1
 returnJson :: (Monad m, J.ToJSON a) => a -> m J.Value
 returnJson = return . J.toJSON
 
+#if MIN_VERSION_aeson(0, 11, 0)
+-- | Convert a value to a JSON representation via aeson\'s 'J.toEncoding' function.
+--
+-- @since 1.4.21
+returnJsonEncoding :: (Monad m, J.ToJSON a) => a -> m J.Encoding
+returnJsonEncoding = return . J.toEncoding
+#endif
+
 -- | Provide a JSON representation for usage with 'selectReps', using aeson\'s
--- 'J.toJSON' function to perform the conversion.
+-- 'J.toJSON' (aeson >= 0.11: 'J.toEncoding') function to perform the conversion.
 --
--- Since 1.2.1
+-- @since 1.2.1
 provideJson :: (Monad m, J.ToJSON a) => a -> Writer (Endo [ProvidedRep m]) ()
+#if MIN_VERSION_aeson(0, 11, 0)
+provideJson = provideRep . return . J.toEncoding
+#else
 provideJson = provideRep . return . J.toJSON
+#endif
 
 -- | Parse the request body to a data type as a JSON value.  The
 -- data type must support conversion from JSON via 'J.FromJSON'.
@@ -91,7 +113,7 @@
 -- twice will result in a parse error on the second call, since the request
 -- body will no longer be available.
 --
--- /Since: 0.3.0/
+-- @since 0.3.0
 parseJsonBody :: (MonadHandler m, J.FromJSON a) => m (J.Result a)
 parseJsonBody = do
     eValue <- rawRequestBody $$ runCatchC (sinkParser JP.value')
@@ -129,9 +151,32 @@
                => Route (HandlerSite m) -- ^ Redirect target
                -> a            -- ^ Data to send via JSON
                -> m J.Value
-jsonOrRedirect r j = do
+jsonOrRedirect = jsonOrRedirect' J.toJSON
+
+#if MIN_VERSION_aeson(0, 11, 0)
+-- | jsonEncodingOrRedirect simplifies the scenario where a POST handler sends a different
+-- response based on Accept headers:
+--
+--     1. 200 with JSON data if the client prefers
+--     @application\/json@ (e.g. AJAX, see 'acceptsJSON').
+--
+--     2. 3xx otherwise, following the PRG pattern.
+-- @since 1.4.21
+jsonEncodingOrRedirect :: (MonadHandler m, J.ToJSON a)
+            => Route (HandlerSite m) -- ^ Redirect target
+            -> a            -- ^ Data to send via JSON
+            -> m J.Encoding
+jsonEncodingOrRedirect = jsonOrRedirect' J.toEncoding
+#endif
+
+jsonOrRedirect' :: (MonadHandler m, J.ToJSON a)
+            => (a -> b)
+            -> Route (HandlerSite m) -- ^ Redirect target
+            -> a            -- ^ Data to send via JSON
+            -> m b
+jsonOrRedirect' f r j = do
     q <- acceptsJson
-    if q then return (J.toJSON j)
+    if q then return (f j)
          else redirect r
 
 -- | Returns @True@ if the client prefers @application\/json@ as
diff --git a/Yesod/Routes/Parse.hs b/Yesod/Routes/Parse.hs
--- a/Yesod/Routes/Parse.hs
+++ b/Yesod/Routes/Parse.hs
@@ -58,7 +58,7 @@
     { quoteExp = lift . resourcesFromString
     }
 
--- | Convert a multi-line string to a set of resources. See documentation for
+-- | Converts a multi-line string to a set of resources. See documentation for
 -- the format of this string. This is a partial function which calls 'error' on
 -- invalid input.
 resourcesFromString :: String -> [ResourceTree String]
diff --git a/yesod-core.cabal b/yesod-core.cabal
--- a/yesod-core.cabal
+++ b/yesod-core.cabal
@@ -1,5 +1,5 @@
 name:            yesod-core
-version:         1.4.20.2
+version:         1.4.21
 license:         MIT
 license-file:    LICENSE
 author:          Michael Snoyman <michael@snoyman.com>
@@ -26,7 +26,7 @@
                    , time                  >= 1.1.4
                    , wai                   >= 3.0
                    , wai-extra             >= 3.0.7
-                   , bytestring            >= 0.9.1.4
+                   , bytestring            >= 0.10
                    , text                  >= 0.7
                    , template-haskell
                    , path-pieces           >= 0.1.2    && < 0.3