diff --git a/Annex/AdjustedBranch.hs b/Annex/AdjustedBranch.hs
index 1f1daecbc9..24f60b260d 100644
--- a/Annex/AdjustedBranch.hs
+++ b/Annex/AdjustedBranch.hs
@@ -5,7 +5,7 @@
  - Licensed under the GNU AGPL version 3 or higher.
  -}
 
-{-# LANGUAGE BangPatterns #-}
+{-# LANGUAGE BangPatterns, OverloadedStrings #-}
 
 module Annex.AdjustedBranch (
 	Adjustment(..),
@@ -61,6 +61,7 @@ import qualified Database.Keys
 import Config
 
 import qualified Data.Map as M
+import qualified Data.ByteString as S
 
 -- How to perform various adjustments to a TreeItem.
 class AdjustTreeItem t where
@@ -128,7 +129,7 @@ newtype BasisBranch = BasisBranch Ref
 -- refs/basis/adjusted/master(unlocked).
 basisBranch :: AdjBranch -> BasisBranch
 basisBranch (AdjBranch adjbranch) = BasisBranch $
-	Ref ("refs/basis/" ++ fromRef (Git.Ref.base adjbranch))
+	Ref ("refs/basis/" <> fromRef' (Git.Ref.base adjbranch))
 
 getAdjustment :: Branch -> Maybe Adjustment
 getAdjustment = fmap fst . adjustedToOriginal
@@ -405,7 +406,8 @@ mergeToAdjustedBranch tomerge (origbranch, adj) mergeconfig canresolvemerge comm
 					<||> (resolveMerge (Just updatedorig) tomerge True <&&> commitResolvedMerge commitmode)
 				if merged
 					then do
-						!mergecommit <- liftIO $ extractSha <$> readFile (tmpgit </> "HEAD")
+						!mergecommit <- liftIO $ extractSha
+							<$> S.readFile (tmpgit </> "HEAD")
 						-- This is run after the commit lock is dropped.
 						return $ postmerge mergecommit
 					else return $ return False
diff --git a/Annex/Branch.hs b/Annex/Branch.hs
index f4b5ce1a1f..5870b6ad21 100644
--- a/Annex/Branch.hs
+++ b/Annex/Branch.hs
@@ -5,6 +5,8 @@
  - Licensed under the GNU AGPL version 3 or higher.
  -}
 
+{-# LANGUAGE OverloadedStrings #-}
+
 module Annex.Branch (
 	fullname,
 	name,
@@ -57,7 +59,7 @@ import qualified Git.LsTree
 import Git.LsTree (lsTreeParams)
 import qualified Git.HashObject
 import Annex.HashObject
-import Git.Types (Ref(..), fromRef, RefDate, TreeItemType(..))
+import Git.Types (Ref(..), fromRef, fromRef', RefDate, TreeItemType(..))
 import Git.FilePath
 import Annex.CatFile
 import Annex.Perms
@@ -79,11 +81,11 @@ name = Git.Ref "git-annex"
 
 {- Fully qualified name of the branch. -}
 fullname :: Git.Ref
-fullname = Git.Ref $ "refs/heads/" ++ fromRef name
+fullname = Git.Ref $ "refs/heads/" <> fromRef' name
 
 {- Branch's name in origin. -}
 originname :: Git.Ref
-originname = Git.Ref $ "origin/" ++ fromRef name
+originname = Git.Ref $ "origin/" <> fromRef' name
 
 {- Does origin/git-annex exist? -}
 hasOrigin :: Annex Bool
@@ -329,9 +331,9 @@ commitIndex' jl branchref message basemessage retrynum parents = do
   where
 	-- look for "parent ref" lines and return the refs
 	commitparents = map (Git.Ref . snd) . filter isparent .
-		map (toassoc . decodeBL) . L.split newline
+		map (toassoc . L.toStrict) . L.split newline
 	newline = fromIntegral (ord '\n')
-	toassoc = separate (== ' ')
+	toassoc = separate' (== (fromIntegral (ord ' ')))
 	isparent (k,_) = k == "parent"
 		
 	{- The race can be detected by checking the commit's
@@ -440,8 +442,8 @@ forceUpdateIndex jl branchref = do
 needUpdateIndex :: Git.Ref -> Annex Bool
 needUpdateIndex branchref = do
 	f <- fromRepo gitAnnexIndexStatus
-	committedref <- Git.Ref . firstLine <$>
-		liftIO (catchDefaultIO "" $ readFileStrict f)
+	committedref <- Git.Ref . firstLine' <$>
+		liftIO (catchDefaultIO mempty $ B.readFile f)
 	return (committedref /= branchref)
 
 {- Record that the branch's index has been updated to correspond to a
@@ -623,11 +625,12 @@ ignoreRefs rs = do
 		unlines $ map fromRef $ S.elems s
 
 getIgnoredRefs :: Annex (S.Set Git.Sha)
-getIgnoredRefs = S.fromList . mapMaybe Git.Sha.extractSha . lines <$> content
+getIgnoredRefs = 
+	S.fromList . mapMaybe Git.Sha.extractSha . B8.lines <$> content
   where
 	content = do
 		f <- fromRepo gitAnnexIgnoredRefs
-		liftIO $ catchDefaultIO "" $ readFile f
+		liftIO $ catchDefaultIO mempty $ B.readFile f
 
 addMergedRefs :: [(Git.Sha, Git.Branch)] -> Annex ()
 addMergedRefs [] = return ()
diff --git a/Annex/Export.hs b/Annex/Export.hs
index 16786476de..0d2ff65235 100644
--- a/Annex/Export.hs
+++ b/Annex/Export.hs
@@ -14,7 +14,6 @@ import Types.Key
 import qualified Git
 import qualified Types.Remote as Remote
 import Messages
-import Utility.FileSystemEncoding
 
 import Control.Applicative
 import Data.Maybe
@@ -34,7 +33,7 @@ exportKey sha = mk <$> catKey sha
   where
 	mk (Just k) = AnnexKey k
 	mk Nothing = GitKey $ mkKey $ \k -> k
-		{ keyName = encodeBS $ Git.fromRef sha
+		{ keyName = Git.fromRef' sha
 		, keyVariety = SHA1Key (HasExt False)
 		, keySize = Nothing
 		, keyMtime = Nothing
diff --git a/Annex/Import.hs b/Annex/Import.hs
index e346ff210e..9d21a27aff 100644
--- a/Annex/Import.hs
+++ b/Annex/Import.hs
@@ -122,7 +122,9 @@ buildImportCommit remote importtreeconfig importcommitconfig importable =
 			Nothing -> pure committedtree
 			Just dir -> 
 				let subtreeref = Ref $
-					fromRef committedtree ++ ":" ++ fromRawFilePath (getTopFilePath dir)
+					fromRef' committedtree 
+						<> ":"
+						<> getTopFilePath dir
 				in fromMaybe emptyTree
 					<$> inRepo (Git.Ref.tree subtreeref)
 		updateexportdb importedtree
diff --git a/Annex/TaggedPush.hs b/Annex/TaggedPush.hs
index b2368dba14..cde24cdb74 100644
--- a/Annex/TaggedPush.hs
+++ b/Annex/TaggedPush.hs
@@ -5,6 +5,8 @@
  - Licensed under the GNU AGPL version 3 or higher.
  -}
 
+{-# LANGUAGE OverloadedStrings #-}
+
 module Annex.TaggedPush where
 
 import Annex.Common
@@ -16,6 +18,8 @@ import qualified Git.Command
 import qualified Git.Branch
 import Utility.Base64
 
+import qualified Data.ByteString as S
+
 {- Converts a git branch into a branch that is tagged with a UUID, typically
  - the UUID of the repo that will be pushing it, and possibly with other
  - information.
@@ -31,11 +35,11 @@ import Utility.Base64
  - refs, per git-check-ref-format.
  -}
 toTaggedBranch :: UUID -> Maybe String -> Git.Branch -> Git.Ref
-toTaggedBranch u info b = Git.Ref $ intercalate "/" $ catMaybes
+toTaggedBranch u info b = Git.Ref $ S.intercalate "/" $ catMaybes
 	[ Just "refs/synced"
 	, Just $ fromUUID u
-	, toB64 <$> info
-	, Just $ Git.fromRef $ Git.Ref.base b
+	, toB64' . encodeBS <$> info
+	, Just $ Git.fromRef' $ Git.Ref.base b
 	]
 
 fromTaggedBranch :: Git.Ref -> Maybe (UUID, Maybe String)
diff --git a/Assistant/Threads/Merger.hs b/Assistant/Threads/Merger.hs
index ac9435122a..49c3956f10 100644
--- a/Assistant/Threads/Merger.hs
+++ b/Assistant/Threads/Merger.hs
@@ -109,6 +109,6 @@ isAnnexBranch f = n `isSuffixOf` f
 	n = '/' : Git.fromRef Annex.Branch.name
 
 fileToBranch :: FilePath -> Git.Ref
-fileToBranch f = Git.Ref $ "refs" </> base
+fileToBranch f = Git.Ref $ encodeBS' $ "refs" </> base
   where
 	base = Prelude.last $ split "/refs/" f
diff --git a/Assistant/Threads/Watcher.hs b/Assistant/Threads/Watcher.hs
index 80523b5e55..0956f59ba5 100644
--- a/Assistant/Threads/Watcher.hs
+++ b/Assistant/Threads/Watcher.hs
@@ -330,7 +330,7 @@ addLink :: FilePath -> FilePath -> Maybe Key -> Assistant (Maybe Change)
 addLink file link mk = do
 	debug ["add symlink", file]
 	liftAnnex $ do
-		v <- catObjectDetails $ Ref $ ':':file
+		v <- catObjectDetails $ Ref $ encodeBS' $ ':':file
 		case v of
 			Just (currlink, sha, _type)
 				| s2w8 link == L.unpack currlink ->
diff --git a/Command/Export.hs b/Command/Export.hs
index f66c512d25..97c9014f51 100644
--- a/Command/Export.hs
+++ b/Command/Export.hs
@@ -37,6 +37,7 @@ import Utility.Tmp
 import Utility.Metered
 import Utility.Matcher
 
+import qualified Data.ByteString.Char8 as S8
 import qualified Data.ByteString.Lazy as L
 import qualified Data.Map as M
 import Control.Concurrent
@@ -112,7 +113,7 @@ getExportCommit r treeish
 		return (fmap (tb, ) commitsha)
 	| otherwise = return Nothing
   where
-	baseref = Ref $ takeWhile (/= ':') $ fromRef $ 
+	baseref = Ref $ S8.takeWhile (/= ':') $ fromRef' $ 
 		Git.Ref.removeBase refsheads treeish
 	refsheads = "refs/heads"
 
diff --git a/Command/FindRef.hs b/Command/FindRef.hs
index eb74928f4c..27dfcbe07a 100644
--- a/Command/FindRef.hs
+++ b/Command/FindRef.hs
@@ -22,6 +22,6 @@ seek o = Find.seek o'
   where
 	o' = o 
 		{ Find.keyOptions = Just $ WantBranchKeys $
-			map Git.Ref (Find.findThese o)
+			map (Git.Ref . encodeBS') (Find.findThese o)
 		, Find.findThese = []
 		}
diff --git a/Command/Import.hs b/Command/Import.hs
index 5447df5bff..5d1c87c320 100644
--- a/Command/Import.hs
+++ b/Command/Import.hs
@@ -66,7 +66,7 @@ optParser desc = do
 			[bs] -> 
 				let (branch, subdir) = separate (== ':') bs
 				in RemoteImportOptions r
-					(Ref branch)
+					(Ref (encodeBS' branch))
 					(if null subdir then Nothing else Just subdir)
 			_ -> giveup "expected BRANCH[:SUBDIR]"
 
diff --git a/Command/Info.hs b/Command/Info.hs
index 3448ee6ef2..7df42fa39a 100644
--- a/Command/Info.hs
+++ b/Command/Info.hs
@@ -181,7 +181,7 @@ dirInfo o dir = showCustom (unwords ["info", dir]) $ do
 
 treeishInfo :: InfoOptions -> String -> Annex ()
 treeishInfo o t = do
-	mi <- getTreeStatInfo o (Git.Ref t)
+	mi <- getTreeStatInfo o (Git.Ref (encodeBS' t))
 	case mi of
 		Nothing -> noInfo t
 		Just i -> showCustom (unwords ["info", t]) $ do
diff --git a/Command/Log.hs b/Command/Log.hs
index 5597bfbf47..b2a7ea7e12 100644
--- a/Command/Log.hs
+++ b/Command/Log.hs
@@ -264,7 +264,8 @@ parseGitRawLog config = parse epoch
 parseRawChangeLine :: String -> Maybe (Git.Ref, Git.Ref)
 parseRawChangeLine = go . words
   where
-	go (_:_:oldsha:newsha:_) = Just (Git.Ref oldsha, Git.Ref newsha)
+	go (_:_:oldsha:newsha:_) = 
+		Just (Git.Ref (encodeBS oldsha), Git.Ref (encodeBS newsha))
 	go _ = Nothing
 
 parseTimeStamp :: String -> POSIXTime
diff --git a/Command/Merge.hs b/Command/Merge.hs
index fe1119dc8a..ed075ad876 100644
--- a/Command/Merge.hs
+++ b/Command/Merge.hs
@@ -26,7 +26,7 @@ seek [] = do
 	commandAction mergeSyncedBranch
 seek bs = do
 	prepMerge
-	forM_ bs (commandAction . mergeBranch . Git.Ref)
+	forM_ bs (commandAction . mergeBranch . Git.Ref . encodeBS')
 
 mergeAnnexBranch :: CommandStart
 mergeAnnexBranch = starting "merge" (ActionItemOther (Just "git-annex")) $ do
diff --git a/Command/ResolveMerge.hs b/Command/ResolveMerge.hs
index e3d9829be8..10f5f98901 100644
--- a/Command/ResolveMerge.hs
+++ b/Command/ResolveMerge.hs
@@ -13,6 +13,8 @@ import Git.Sha
 import qualified Git.Branch
 import Annex.AutoMerge
 
+import qualified Data.ByteString as S
+
 cmd :: Command
 cmd = command "resolvemerge" SectionPlumbing
 	"resolve merge conflicts"
@@ -27,7 +29,7 @@ start = starting "resolvemerge" (ActionItemOther Nothing) $ do
 	d <- fromRawFilePath <$> fromRepo Git.localGitDir
 	let merge_head = d </> "MERGE_HEAD"
 	them <- fromMaybe (error nomergehead) . extractSha
-		<$> liftIO (readFile merge_head)
+		<$> liftIO (S.readFile merge_head)
 	ifM (resolveMerge (Just us) them False)
 		( do
 			void $ commitResolvedMerge Git.Branch.ManualCommit
diff --git a/Command/Sync.hs b/Command/Sync.hs
index 49ec61cb52..42afe518a9 100644
--- a/Command/Sync.hs
+++ b/Command/Sync.hs
@@ -72,6 +72,8 @@ import Utility.Process.Transcript
 
 import Control.Concurrent.MVar
 import qualified Data.Map as M
+import qualified Data.ByteString as S
+import Data.Char
 
 cmd :: Command
 cmd = withGlobalOptions [jobsOption] $
@@ -444,11 +446,11 @@ importRemote o mergeconfig remote currbranch
 	| otherwise = case remoteAnnexTrackingBranch (Remote.gitconfig remote) of
 		Nothing -> noop
 		Just tb -> do
-			let (b, s) = separate (== ':') (Git.fromRef tb)
+			let (b, p) = separate' (== (fromIntegral (ord ':'))) (Git.fromRef' tb)
 			let branch = Git.Ref b
-			let subdir = if null s
+			let subdir = if S.null p
 				then Nothing
-				else Just (asTopFilePath (toRawFilePath s))
+				else Just (asTopFilePath p)
 			Command.Import.seekRemote remote branch subdir
 			void $ mergeRemote remote currbranch mergeconfig o
   where
diff --git a/Command/Uninit.hs b/Command/Uninit.hs
index c64d4aa2dc..db7d25a7a8 100644
--- a/Command/Uninit.hs
+++ b/Command/Uninit.hs
@@ -35,7 +35,7 @@ check = do
 	whenM ((/=) <$> liftIO (absPath top) <*> liftIO (absPath currdir)) $
 		giveup "can only run uninit from the top of the git repository"
   where
-	current_branch = Git.Ref . Prelude.head . lines . decodeBS' <$> revhead
+	current_branch = Git.Ref . encodeBS' . Prelude.head . lines . decodeBS' <$> revhead
 	revhead = inRepo $ Git.Command.pipeReadStrict
 		[Param "rev-parse", Param "--abbrev-ref", Param "HEAD"]
 
diff --git a/Command/Unused.hs b/Command/Unused.hs
index b68452d5c8..4b2de82597 100644
--- a/Command/Unused.hs
+++ b/Command/Unused.hs
@@ -5,12 +5,10 @@
  - Licensed under the GNU AGPL version 3 or higher.
  -}
 
-{-# LANGUAGE BangPatterns #-}
+{-# LANGUAGE BangPatterns, OverloadedStrings #-}
 
 module Command.Unused where
 
-import qualified Data.Map as M
-
 import Command
 import Logs.Unused
 import Annex.Content
@@ -37,6 +35,11 @@ import Annex.BloomFilter
 import qualified Database.Keys
 import Annex.InodeSentinal
 
+import qualified Data.Map as M
+import qualified Data.ByteString as S
+import qualified Data.ByteString.Char8 as S8
+import Data.Char
+
 cmd :: Command
 cmd = command "unused" SectionMaintenance "look for unused file content"
 	paramNothing (seek <$$> optParser)
@@ -221,8 +224,7 @@ withKeysReferenced' mdir initial a = do
 
 withKeysReferencedDiffGitRefs :: RefSpec -> (Key -> Annex ()) -> Annex ()
 withKeysReferencedDiffGitRefs refspec a = do
-	rs <- relevantrefs . decodeBS'
-		<$> inRepo (Git.Command.pipeReadStrict [Param "show-ref"])
+	rs <- relevantrefs <$> inRepo (Git.Command.pipeReadStrict [Param "show-ref"])
 	shaHead <- maybe (return Nothing) (inRepo . Git.Ref.sha)
 		=<< inRepo Git.Branch.currentUnsafe
 	let haveHead = any (\(shaRef, _) -> Just shaRef == shaHead) rs
@@ -233,12 +235,12 @@ withKeysReferencedDiffGitRefs refspec a = do
   where
 	relevantrefs = map (\(r, h) -> (Git.Ref r, Git.Ref h)) .
 		filter ourbranches .
-		map (separate (== ' ')) .
-		lines
+		map (separate' (== (fromIntegral (ord ' ')))) .
+		S8.lines
 	nubRefs = nubBy (\(x, _) (y, _) -> x == y)
-	ourbranchend = '/' : Git.fromRef Annex.Branch.name
-	ourbranches (_, b) = not (ourbranchend `isSuffixOf` b)
-		&& not ("refs/synced/" `isPrefixOf` b)
+	ourbranchend = S.cons (fromIntegral (ord '/')) (Git.fromRef' Annex.Branch.name)
+	ourbranches (_, b) = not (ourbranchend `S.isSuffixOf` b)
+		&& not ("refs/synced/" `S.isPrefixOf` b)
 		&& not (is_branchView (Git.Ref b))
 	getreflog rs = inRepo $ Git.RefLog.getMulti rs
 
diff --git a/Git/Ref.hs b/Git/Ref.hs
index 33922d1e30..104a1db715 100644
--- a/Git/Ref.hs
+++ b/Git/Ref.hs
@@ -26,7 +26,7 @@ headFile :: Repo -> FilePath
 headFile r = fromRawFilePath (localGitDir r) </> "HEAD"
 
 setHeadRef :: Ref -> Repo -> IO ()
-setHeadRef ref r = writeFile (headFile r) ("ref: " ++ fromRef ref)
+setHeadRef ref r = S.writeFile (headFile r) ("ref: " <> fromRef' ref)
 
 {- Converts a fully qualified git ref into a user-visible string. -}
 describe :: Ref -> String
@@ -55,7 +55,7 @@ removeBase dir r
  - refs/heads/master, yields a version of that ref under the directory,
  - such as refs/remotes/origin/master. -}
 underBase :: String -> Ref -> Ref
-underBase dir r = Ref $ encodeBS' $ dir ++ "/" ++ fromRef (base r)
+underBase dir r = Ref $ encodeBS dir <> "/" <> fromRef' (base r)
 
 {- Convert a branch such as "master" into a fully qualified ref. -}
 branchRef :: Branch -> Ref
diff --git a/Logs/Export.hs b/Logs/Export.hs
index aadd1b9c4a..586c789e86 100644
--- a/Logs/Export.hs
+++ b/Logs/Export.hs
@@ -158,12 +158,12 @@ buildExported exported = go (exportedTreeish exported : incompleteExportedTreeis
   where
 	go [] = mempty
 	go (r:rs) = rref r <> mconcat [ charUtf8 ' ' <> rref r' | r' <- rs ]
-	rref r = byteString (encodeBS' (Git.fromRef r))
+	rref = byteString . Git.fromRef'
 
 exportedParser :: A.Parser Exported
 exportedParser = Exported <$> refparser <*> many refparser
   where
-	refparser = (Git.Ref . decodeBS <$> A8.takeWhile1 (/= ' ') )
+	refparser = (Git.Ref <$> A8.takeWhile1 (/= ' ') )
 		<* ((const () <$> A8.char ' ') <|> A.endOfInput)
 
 logExportExcluded :: UUID -> ((Git.Tree.TreeItem -> IO ()) -> Annex a) -> Annex a
diff --git a/Test.hs b/Test.hs
index 29f891dc4e..04d36424e9 100644
--- a/Test.hs
+++ b/Test.hs
@@ -1664,7 +1664,7 @@ test_add_subdirs = intmpclonerepo $ do
 	unlessM (hasUnlockedFiles <$> getTestMode) $ do
 		git_annex "sync" [] @? "sync failed"
 		l <- annexeval $ Utility.FileSystemEncoding.decodeBL
-			<$> Annex.CatFile.catObject (Git.Types.Ref "HEAD:dir/foo")
+			<$> Annex.CatFile.catObject (Git.Types.Ref (encodeBS "HEAD:dir/foo"))
 		"../.git/annex/" `isPrefixOf` l @? ("symlink from subdir to .git/annex is wrong: " ++ l)
 
 	createDirectory "dir2"
diff --git a/Upgrade/V2.hs b/Upgrade/V2.hs
index 4a70a05d1a..24d92e4ffc 100644
--- a/Upgrade/V2.hs
+++ b/Upgrade/V2.hs
@@ -92,7 +92,8 @@ logFiles dir = return . filter (".log" `isSuffixOf`)
 
 push :: Annex ()
 push = do
-	origin_master <- inRepo $ Git.Ref.exists $ Git.Ref "origin/master"
+	origin_master <- inRepo $ Git.Ref.exists $ 
+		Git.Ref $ encodeBS' "origin/master"
 	origin_gitannex <- Annex.Branch.hasOrigin
 	case (origin_master, origin_gitannex) of
 		(_, True) -> do
diff --git a/doc/todo/optimise_by_converting_Ref_to_ByteString.mdwn b/doc/todo/optimise_by_converting_Ref_to_ByteString.mdwn
index 6434c4de3d..8b9f79c2da 100644
--- a/doc/todo/optimise_by_converting_Ref_to_ByteString.mdwn
+++ b/doc/todo/optimise_by_converting_Ref_to_ByteString.mdwn
@@ -3,3 +3,9 @@ to contain a ByteString, rather than a String, would eliminate a
 fromRawFilePath that uses about 1% of runtime.
 
 [[!tag confirmed]]
+
+> Well, I did the conversion. Running that command does not seem to have 
+> sped up by any appreciable amount. But, I did notice several places where
+> using ByteString is certainly more efficient. It may just be that it
+> doesn't matter if git-annex is IO bound etc. Still, glad I did it.
+> [[done]] --[[Joey]]