diff --git a/CHANGELOG b/CHANGELOG
index d822869bcf..00ec380f96 100644
--- a/CHANGELOG
+++ b/CHANGELOG
@@ -1,3 +1,10 @@
+git-annex (8.20210715) UNRELEASED; urgency=medium
+
+  * whereused: New command, finds what files use a key, or where a key
+    was used historically.
+
+ -- Joey Hess <id@joeyh.name>  Wed, 14 Jul 2021 14:26:36 -0400
+
 git-annex (8.20210714) upstream; urgency=medium
 
   * assistant: Avoid unncessary git repository repair in a situation where
diff --git a/CmdLine/GitAnnex.hs b/CmdLine/GitAnnex.hs
index fe40081483..807aa14083 100644
--- a/CmdLine/GitAnnex.hs
+++ b/CmdLine/GitAnnex.hs
@@ -72,6 +72,7 @@ import qualified Command.FilterBranch
 import qualified Command.Find
 import qualified Command.FindRef
 import qualified Command.Whereis
+import qualified Command.WhereUsed
 import qualified Command.List
 import qualified Command.Log
 import qualified Command.Merge
@@ -207,6 +208,7 @@ cmds testoptparser testrunner mkbenchmarkgenerator = map addGitAnnexGlobalOption
 	, Command.Find.cmd
 	, Command.FindRef.cmd
 	, Command.Whereis.cmd
+	, Command.WhereUsed.cmd
 	, Command.List.cmd
 	, Command.Log.cmd
 	, Command.Merge.cmd
diff --git a/Command/WhereUsed.hs b/Command/WhereUsed.hs
new file mode 100644
index 0000000000..4534d90e1a
--- /dev/null
+++ b/Command/WhereUsed.hs
@@ -0,0 +1,68 @@
+{- git-annex command
+ -
+ - Copyright 2021 Joey Hess <id@joeyh.name>
+ -
+ - Licensed under the GNU AGPL version 3 or higher.
+ -}
+
+module Command.WhereUsed where
+
+import Command
+import Git.FilePath
+import Annex.CatFile
+import Database.Keys
+
+cmd :: Command
+cmd = noCommit $ withGlobalOptions [annexedMatchingOptions] $
+	command "whereused" SectionQuery
+		"lists repositories that have file content"
+		paramNothing (seek <$$> optParser)
+
+data WhereUsedOptions = WhereUsedOptions
+	{ keyOptions :: KeyOptions
+	, historicalOption :: Bool
+	}
+
+optParser :: CmdParamsDesc -> Parser WhereUsedOptions
+optParser _desc = WhereUsedOptions
+	<$> (parseUnusedKeysOption <|> parseSpecificKeyOption)
+	<*> switch
+		( long "historical"
+		<> help "find historical uses"
+		)
+
+seek :: WhereUsedOptions -> CommandSeek
+seek o = withKeyOptions (Just (keyOptions o)) False dummyfileseeker
+	(commandAction . start o) dummyfilecommandseek (WorkTreeItems [])
+  where
+	dummyfileseeker = AnnexedFileSeeker
+		{ startAction = \_ _ _ -> return Nothing
+		, checkContentPresent = Nothing
+		, usesLocationLog = False
+		}
+	dummyfilecommandseek = const noop
+
+start :: WhereUsedOptions -> (SeekInput, Key, ActionItem) -> CommandStart
+start o (_, key, _) = startingCustomOutput key $ do
+	fs <- filterM stillassociated 
+		=<< mapM (fromRepo . fromTopFilePath)
+		=<< getAssociatedFiles key
+	liftIO $ forM_ fs $ display key . fromRawFilePath
+
+	when (historicalOption o && null fs) $
+		findHistorical key
+
+	next $ return True
+  where
+	-- Some associated files that are in the keys database may no
+	-- longer correspond to files in the repository.
+	stillassociated f = catKeyFile f >>= \case
+		Just k | k == key -> return True
+		_ -> return False
+
+display :: Key -> FilePath -> IO ()
+display key f = putStrLn (serializeKey key ++ " " ++ f)
+
+findHistorical :: Key -> Annex ()
+findHistorical key = do
+	error "TODO"
diff --git a/doc/git-annex-whereused.mdwn b/doc/git-annex-whereused.mdwn
index d142aae7fc..385720c5e1 100644
--- a/doc/git-annex-whereused.mdwn
+++ b/doc/git-annex-whereused.mdwn
@@ -4,7 +4,7 @@ git-annex whereused - find what files use, or used a key
 
 # SYNOPSIS
 
-git annex whereused `--key=K|--unused`
+git annex whereused `--key=keyname|--unused`
 
 # DESCRIPTION
 
diff --git a/doc/git-annex.mdwn b/doc/git-annex.mdwn
index 82b6925120..ca5d69fe34 100644
--- a/doc/git-annex.mdwn
+++ b/doc/git-annex.mdwn
@@ -373,10 +373,6 @@ content from the key-value store.
   
   See [[git-annex-addunused]](1) for details.
 
-* `whereused`
-
-  Finds what files use, or used a key.
-
 * `fix [path ...]`
 
   Fixes up symlinks that have become broken to again point to annexed content.
@@ -451,6 +447,10 @@ content from the key-value store.
   
   See [[git-annex-list]](1) for details.
 
+* `whereused`
+
+  Finds what files use, or used a key.
+
 * `log [path ...]`
 
   Displays the location log for the specified file or files,
diff --git a/git-annex.cabal b/git-annex.cabal
index bf6df7557e..6b5684ea53 100644
--- a/git-annex.cabal
+++ b/git-annex.cabal
@@ -144,6 +144,7 @@ Extra-Source-Files:
   doc/git-annex-watch.mdwn
   doc/git-annex-webapp.mdwn
   doc/git-annex-whereis.mdwn
+  doc/git-annex-whereused.mdwn
   doc/git-remote-tor-annex.mdwn
   doc/logo.svg
   doc/logo_16x16.png
@@ -830,6 +831,7 @@ Executable git-annex
     Command.View
     Command.Wanted
     Command.Whereis
+    Command.WhereUsed
     Common
     Config
     Config.Cost