diff --git a/Data/Conduit/Binary.hs b/Data/Conduit/Binary.hs
--- a/Data/Conduit/Binary.hs
+++ b/Data/Conduit/Binary.hs
@@ -1,4 +1,4 @@
-{-# LANGUAGE CPP #-}
+{-# LANGUAGE CPP, RankNTypes #-}
 -- | Functions for interacting with bytes.
 module Data.Conduit.Binary
     ( -- * Files and @Handle@s
diff --git a/Data/Conduit/Internal.hs b/Data/Conduit/Internal.hs
--- a/Data/Conduit/Internal.hs
+++ b/Data/Conduit/Internal.hs
@@ -429,6 +429,12 @@
 
 -- | Transform the monad that a @Pipe@ lives in.
 --
+-- Note that the monad transforming function will be run multiple times,
+-- resulting in unintuitive behavior in some cases. For a fuller treatment,
+-- please see:
+--
+-- <https://github.com/snoyberg/conduit/wiki/Dealing-with-monad-transformers>
+--
 -- Since 0.4.0
 transPipe :: Monad m => (forall a. m a -> n a) -> Pipe l i o u m r -> Pipe l i o u n r
 transPipe f (HaveOutput p c o) = HaveOutput (transPipe f p) (f c) o
diff --git a/Data/Conduit/List.hs b/Data/Conduit/List.hs
--- a/Data/Conduit/List.hs
+++ b/Data/Conduit/List.hs
@@ -18,6 +18,7 @@
       -- * Sinks
       -- ** Pure
     , fold
+    , foldMap
     , take
     , drop
     , head
@@ -59,6 +60,7 @@
     , maybe
     , either
     )
+import Data.Monoid (Monoid, mempty, mappend)
 import Data.Conduit hiding (Source, Sink, Conduit, Pipe)
 import Data.Conduit.Internal (sourceList)
 import Control.Monad (when, (<=<))
@@ -137,6 +139,17 @@
         go a = do
             accum' <- lift $ f accum a
             accum' `seq` loop accum'
+
+-- | A monoidal strict left fold.
+--
+-- Since 0.5.3
+foldMap :: (Monad m, Monoid b)
+        => (a -> b)
+        -> GSink a m b
+foldMap f =
+    fold combiner mempty
+  where
+    combiner accum = mappend accum . f
 
 -- | Apply the action to all values in the stream.
 --
diff --git a/Data/Conduit/Text.hs b/Data/Conduit/Text.hs
--- a/Data/Conduit/Text.hs
+++ b/Data/Conduit/Text.hs
@@ -1,4 +1,4 @@
-{-# LANGUAGE DeriveDataTypeable #-}
+{-# LANGUAGE DeriveDataTypeable, RankNTypes #-}
 -- |
 -- Copyright: 2011 Michael Snoyman, 2010-2011 John Millikin
 -- License: MIT
diff --git a/conduit.cabal b/conduit.cabal
--- a/conduit.cabal
+++ b/conduit.cabal
@@ -1,5 +1,5 @@
 Name:                conduit
-Version:             0.5.2.3
+Version:             0.5.2.4
 Synopsis:            Streaming data processing library.
 Description:
     @conduit@ is a solution to the streaming data problem, allowing for production, transformation, and consumption of streams of data in constant memory. It is an alternative to lazy I\/O which guarantees deterministic resource handling, and fits in the same general solution space as @enumerator@/@iteratee@ and @pipes@. For a brief tutorial, please see the "Data.Conduit" module.
@@ -52,7 +52,7 @@
                        Data.Conduit.Util.Sink
                        Data.Conduit.Util.Conduit
   Build-depends:       base                     >= 4.3          && < 5
-                     , resourcet                >= 0.3          && < 0.4
+                     , resourcet                >= 0.3          && < 0.5
                      , lifted-base              >= 0.1          && < 0.2
                      , transformers-base        >= 0.4.1        && < 0.5
                      , monad-control            >= 0.3.1        && < 0.4
diff --git a/test/main.hs b/test/main.hs
--- a/test/main.hs
+++ b/test/main.hs
@@ -90,6 +90,15 @@
             (runST $ CL.sourceList list C.$$ CL.fold (+) (0 :: Int))
             == sum list
 
+    describe "foldMap" $ do
+        it "sums 1..10" $ do
+            Sum x <- CL.sourceList [1..(10 :: Int)] C.$$ CL.foldMap Sum
+            x `shouldBe` sum [1..10]
+
+        it "preserves order" $ do
+            x <- CL.sourceList [[4],[2],[3],[1]] C.$$ CL.foldMap (++[(9 :: Int)])
+            x `shouldBe` [4,9,2,9,3,9,1,9]
+
     describe "unfold" $ do
         it "works" $ do
             let f 0 = Nothing