diff --git a/builder/src/Generate.hs b/builder/src/Generate.hs
index aff6a71f..6eaed5a4 100644
--- a/builder/src/Generate.hs
+++ b/builder/src/Generate.hs
@@ -60,7 +60,10 @@ debug root details (Build.Artifacts pkg ifaces roots modules) =
       let graph_ = objectsToGlobalGraph objects
       graph <- Task.io $ Lamdera.AppConfig.injectConfig graph_
       let mains = gatherMains pkg objects roots
+      esmEnabled <- Task.io $ Lamdera.useEsm
       return $ JS.generate mode graph mains
+        & Lamdera.alternativeImplementationWhen esmEnabled
+            (JS.generateEsm mode graph mains)
 
 
 dev :: FilePath -> Details.Details -> Build.Artifacts -> Task B.Builder
@@ -70,7 +73,10 @@ dev root details (Build.Artifacts pkg _ roots modules) =
       let graph_ = objectsToGlobalGraph objects
       graph <- Task.io $ Lamdera.AppConfig.injectConfig graph_
       let mains = gatherMains pkg objects roots
+      esmEnabled <- Task.io $ Lamdera.useEsm
       return $ JS.generate mode graph mains
+        & Lamdera.alternativeImplementationWhen esmEnabled
+            (JS.generateEsm mode graph mains)
 
 
 prod :: FilePath -> Details.Details -> Build.Artifacts -> Task B.Builder
@@ -84,7 +90,10 @@ prod root details (Build.Artifacts pkg _ roots modules) =
                    & Lamdera.alternativeImplementationWhen longNamesEnabled
                        (Mode.Prod (Mode.legibleFieldNames graph))
       let mains = gatherMains pkg objects roots
+      esmEnabled <- Task.io $ Lamdera.useEsm
       return $ JS.generate mode graph mains
+        & Lamdera.alternativeImplementationWhen esmEnabled
+            (JS.generateEsm mode graph mains)
 
 
 repl :: FilePath -> Details.Details -> Bool -> Build.ReplArtifacts -> N.Name -> Task B.Builder
diff --git a/compiler/src/Generate/JavaScript.hs b/compiler/src/Generate/JavaScript.hs
index d2d0beaf..3d06be5f 100644
--- a/compiler/src/Generate/JavaScript.hs
+++ b/compiler/src/Generate/JavaScript.hs
@@ -1,6 +1,7 @@
 {-# LANGUAGE OverloadedStrings #-}
 module Generate.JavaScript
   ( generate
+  , generateEsm
   , generateForRepl
   , generateForReplEndpoint
   )
@@ -57,6 +58,19 @@ generate mode (Opt.GlobalGraph graph_ _) mains =
   <> "}(this));"
   <> "\n" <> Lamdera.Injection.elmPkgJs mode mains <> "\n"
 
+generateEsm :: Mode.Mode -> Opt.GlobalGraph -> Mains -> B.Builder
+generateEsm mode (Opt.GlobalGraph graph_ _) mains =
+  let
+    graph = Lamdera.Injection.graphModifications mode mains graph_
+    state = Map.foldrWithKey (addMain mode graph) emptyState mains
+  in
+  Functions.functions
+  -- <> perfNote mode -- @NOTE given user never manages JS generation in Lamdera, hide the perf note
+  <> stateToBuilder state
+  <> toMainEsmExports mode mains
+  -- <> Lamdera.Injection.source mode mains -- shadowing not allowed in esm
+  <> "\n" <> Lamdera.Injection.elmPkgJs mode mains <> "\n"
+
 addMain :: Mode.Mode -> Graph -> ModuleName.Canonical -> Opt.Main -> State -> State
 addMain mode graph home _ state =
   addGlobal mode graph state (Opt.Global home "main")
@@ -546,6 +560,13 @@ toMainExports mode mains =
   in
   JsName.toBuilder export <> "(" <> exports <> ");"
 
+toMainEsmExports :: Mode.Mode -> Mains -> B.Builder
+toMainEsmExports mode mains =
+  let
+    exports = generateExports mode (Map.foldrWithKey addToTrie emptyTrie mains)
+  in
+  "export const Elm = " <> exports <> ";"
+
 
 generateExports :: Mode.Mode -> Trie -> B.Builder
 generateExports mode (Trie maybeMain subs) =
diff --git a/extra/Lamdera.hs b/extra/Lamdera.hs
index 8d58f2d5..9d188ddb 100644
--- a/extra/Lamdera.hs
+++ b/extra/Lamdera.hs
@@ -45,6 +45,9 @@ module Lamdera
   , useLongNames_
   , enableLongNames
   , useLongNames
+  , useEsm_
+  , enableEsm
+  , useEsm
   , isTest
   , isLiveMode
   , setLiveMode
@@ -460,6 +463,19 @@ enableLongNames = do
   debug $ "🗜️ enableLongNames"
   modifyMVar_ useLongNames_ (\_ -> pure True)
 
+{-# NOINLINE useEsm_ #-}
+useEsm_ :: MVar Bool
+useEsm_ = unsafePerformIO $ newMVar False
+
+{-# NOINLINE useEsm #-}
+useEsm :: IO Bool
+useEsm = do
+  readMVar useEsm_
+
+enableEsm :: IO ()
+enableEsm = do
+  debug $ "🗜️ enableEsm"
+  modifyMVar_ useEsm_ (\_ -> pure True)
 
 isTest :: IO Bool
 isTest = do
diff --git a/extra/Lamdera/CLI/Check.hs b/extra/Lamdera/CLI/Check.hs
index a5a6c7c0..008dc7c5 100644
--- a/extra/Lamdera/CLI/Check.hs
+++ b/extra/Lamdera/CLI/Check.hs
@@ -599,6 +599,7 @@ buildProductionJsFiles root inProduction_ versionInfo = do
         , _docs = Nothing
         , _noWire = False
         , _optimizeLegible = True
+        , _esm = False
         }
 
     Make.run ["src" </> "LFR.elm"] $
@@ -610,6 +611,7 @@ buildProductionJsFiles root inProduction_ versionInfo = do
         , _docs = Nothing
         , _noWire = False
         , _optimizeLegible = False
+        , _esm = False
         }
 
     Lamdera.AppConfig.writeUsage
@@ -713,6 +715,7 @@ migrationCheck root nextVersion changedTypes = do
           , _docs = Nothing
           , _noWire = False
           , _optimizeLegible = False
+          , _esm = False
           }
 
   -- @TODO this is because the migrationCheck does weird terminal stuff that mangles the display... how to fix this?
diff --git a/extra/Lamdera/Compile.hs b/extra/Lamdera/Compile.hs
index ee78d5be..4bbf9b70 100644
--- a/extra/Lamdera/Compile.hs
+++ b/extra/Lamdera/Compile.hs
@@ -42,6 +42,7 @@ makeOptimizedWithCleanup cleanup root path = do
           , _docs = Nothing
           , _noWire = False
           , _optimizeLegible = False
+          , _esm = False
           }
   wait r
   remove tmp
@@ -69,6 +70,7 @@ make_ root = do
           , _docs = Nothing
           , _noWire = False
           , _optimizeLegible = True
+          , _esm = False
           }
   wait r
   -- The compilation process ends by printing to terminal in a way that overwrites
@@ -98,6 +100,7 @@ makeDev root paths = do
           , _docs = Nothing
           , _noWire = False
           , _optimizeLegible = False
+          , _esm = False
           }
   wait r
   -- The compilation process ends by printing to terminal in a way that overwrites
@@ -127,6 +130,7 @@ makeDevHtml root paths = do
           , _docs = Nothing
           , _noWire = False
           , _optimizeLegible = False
+          , _esm = False
           }
   wait r
   -- The compilation process ends by printing to terminal in a way that overwrites
@@ -158,6 +162,7 @@ makeHarnessDevJs root = do
           , _docs = Nothing
           , _noWire = False
           , _optimizeLegible = False
+          , _esm = False
           }
   wait r
   remove tmp
diff --git a/terminal/src/Main.hs b/terminal/src/Main.hs
index 059a29a2..6ab7eabc 100644
--- a/terminal/src/Main.hs
+++ b/terminal/src/Main.hs
@@ -214,6 +214,7 @@ make =
         |-- flag "docs" Make.docsFile "Generate a JSON file of documentation for a package. Eventually it will be possible to preview docs with `reactor` because it is quite hard to deal with these JSON files directly."
         |-- onOff "no-wire" "Explicitly disable Lamdera's wire codegen."
         |-- onOff "optimize-legible" "Same as --optimize but without identifier shortening, handy for debugging optimised code or for when identifiers are more useful than smaller JS compilations."
+        |-- onOff "esm" "Emit an ECMAScript module instead of an IIFE."
   in
   Terminal.Command "make" Uncommon details example (zeroOrMore elmFile) makeFlags Make.run
 
diff --git a/terminal/src/Make.hs b/terminal/src/Make.hs
index bd41f285..6253cd97 100644
--- a/terminal/src/Make.hs
+++ b/terminal/src/Make.hs
@@ -48,6 +48,7 @@ data Flags =
     , _docs :: Maybe FilePath
     , _noWire :: Bool -- @LAMDERA
     , _optimizeLegible :: Bool -- @LAMDERA
+    , _esm :: Bool -- @LAMDERA
     }
 
 
@@ -69,11 +70,12 @@ type Task a = Task.Task Exit.Make a
 
 
 run :: [FilePath] -> Flags -> IO ()
-run paths flags@(Flags _ _ _ report _ noWire optimizeLegible) =
+run paths flags@(Flags _ _ _ report _ noWire optimizeLegible esm) =
   do  style <- getStyle report
       maybeRoot <- Stuff.findRoot
       Lamdera.onlyWhen noWire Lamdera.disableWire
       Lamdera.onlyWhen optimizeLegible Lamdera.enableLongNames
+      Lamdera.onlyWhen esm Lamdera.enableEsm
       Reporting.attemptWithStyle style Exit.makeToReport $
         case maybeRoot of
           Just root -> runHelp root paths style flags
@@ -81,7 +83,7 @@ run paths flags@(Flags _ _ _ report _ noWire optimizeLegible) =
 
 
 runHelp :: FilePath -> [FilePath] -> Reporting.Style -> Flags -> IO (Either Exit.Make ())
-runHelp root paths style (Flags debug optimize maybeOutput _ maybeDocs _ optimizeLegible) =
+runHelp root paths style (Flags debug optimize maybeOutput _ maybeDocs _ optimizeLegible _) =
   BW.withScope $ \scope ->
   Stuff.withRootLock root $ Task.run $
   do  desiredMode <- getMode debug (optimize || optimizeLegible)
@@ -304,6 +306,7 @@ parseOutput name
   | isDevNull name      = Just DevNull
   | hasExt ".html" name = Just (Html name)
   | hasExt ".js"   name = Just (JS name)
+  | hasExt ".mjs"  name = Just (JS name) -- @LAMDERA
   | otherwise           = Nothing
 
 
@@ -334,11 +337,12 @@ isDevNull name =
 
 -- Clone of run that uses attemptWithStyle_cleanup
 run_cleanup :: IO () -> [FilePath] -> Flags -> IO ()
-run_cleanup cleanup paths flags@(Flags _ _ _ report _ noWire optimizeLegible) =
+run_cleanup cleanup paths flags@(Flags _ _ _ report _ noWire optimizeLegible esm) =
   do  style <- getStyle report
       maybeRoot <- Stuff.findRoot
       Lamdera.onlyWhen noWire Lamdera.disableWire
       Lamdera.onlyWhen optimizeLegible Lamdera.enableLongNames
+      Lamdera.onlyWhen esm Lamdera.enableEsm
       Reporting.attemptWithStyle_cleanup cleanup style Exit.makeToReport $
         case maybeRoot of
           Just root -> runHelp root paths style flags
diff --git a/test/Test/JsOutput.hs b/test/Test/JsOutput.hs
index c055ef25..16d53eaf 100644
--- a/test/Test/JsOutput.hs
+++ b/test/Test/JsOutput.hs
@@ -36,6 +36,7 @@ suite =
                 , _docs = Nothing
                 , _noWire = True
                 , _optimizeLegible = False
+                , _esm = False
                 }
 
         fileContents <- readUtf8Text $ elmStuff ++ "/tmp.js"
@@ -74,6 +75,7 @@ suite =
                 , _docs = Nothing
                 , _noWire = True
                 , _optimizeLegible = False
+                , _esm = False
                 }
 
         fileContents <- readUtf8Text $ elmStuff ++ "/tmp.js"
@@ -123,6 +125,7 @@ suite =
                 , _docs = Nothing
                 , _noWire = True
                 , _optimizeLegible = False
+                , _esm = False
                 }
 
         fileContents <- readUtf8Text $ elmStuff ++ "/tmp.js"
@@ -174,6 +177,7 @@ suite =
                 , _docs = Nothing
                 , _noWire = True
                 , _optimizeLegible = False
+                , _esm = False
                 }
 
         fileContents <- readUtf8Text $ elmStuff ++ "/tmp.js"