diff --git a/grin/grin.cabal b/grin/grin.cabal
index d2e0880e..50e4c951 100644
--- a/grin/grin.cabal
+++ b/grin/grin.cabal
@@ -151,6 +151,7 @@ library
     Transformations.ExtendedSyntax.Optimising.ConstantPropagation
     Transformations.ExtendedSyntax.Optimising.CSE
     Transformations.ExtendedSyntax.Optimising.EvaluatedCaseElimination
+    Transformations.ExtendedSyntax.Optimising.Inlining
     Transformations.ExtendedSyntax.Optimising.GeneralizedUnboxing
     Transformations.ExtendedSyntax.Optimising.SimpleDeadFunctionElimination
     Transformations.ExtendedSyntax.Optimising.SparseCaseOptimisation
@@ -310,6 +311,7 @@ test-suite grin-test
                      Transformations.ExtendedSyntax.Optimising.CopyPropagationSpec
                      Transformations.ExtendedSyntax.Optimising.CSESpec
                      Transformations.ExtendedSyntax.Optimising.EvaluatedCaseEliminationSpec
+                     Transformations.ExtendedSyntax.Optimising.InliningSpec
                      Transformations.ExtendedSyntax.Optimising.GeneralizedUnboxingSpec
                      Transformations.ExtendedSyntax.Optimising.SimpleDeadFunctionEliminationSpec
                      Transformations.ExtendedSyntax.Optimising.SparseCaseOptimisationSpec
diff --git a/grin/src/Transformations/ExtendedSyntax/Optimising/Inlining.hs b/grin/src/Transformations/ExtendedSyntax/Optimising/Inlining.hs
new file mode 100644
index 00000000..eca6f86e
--- /dev/null
+++ b/grin/src/Transformations/ExtendedSyntax/Optimising/Inlining.hs
@@ -0,0 +1,122 @@
+{-# LANGUAGE LambdaCase, TupleSections, RecordWildCards, OverloadedStrings #-}
+module Transformations.ExtendedSyntax.Optimising.Inlining where
+
+
+import Data.Set (Set)
+import Data.Map.Strict (Map)
+import Data.Bifunctor (first)
+import Data.Functor.Foldable as Foldable
+
+import qualified Data.Set as Set
+import qualified Data.Map.Strict as Map
+import qualified Data.Foldable
+
+import Grin.ExtendedSyntax.Grin
+import Grin.ExtendedSyntax.TypeEnv
+import Transformations.ExtendedSyntax.Util
+import Transformations.ExtendedSyntax.Names
+
+-- analysis
+
+data Stat
+  = Stat
+  { bindCount         :: !Int
+  , functionCallCount :: !(Map Name Int)
+  }
+
+instance Semigroup  Stat where (Stat i1 m1) <> (Stat i2 m2) = Stat (i1 + i2) (Map.unionWith (+) m1 m2)
+instance Monoid     Stat where mempty = Stat 0 mempty
+
+selectInlineSet :: Program -> Set Name
+selectInlineSet prog@(Program exts defs) = inlineSet where
+
+  (bindList, callTrees) = unzip
+    [ (Map.singleton name bindCount, (name, functionCallCount))
+    | def@(Def name _ _) <- defs
+    , let Stat{..} = cata folder def
+    ]
+
+  bindSequenceLimit = 100
+
+  -- TODO: limit inline overhead using CALL COUNT * SIZE < LIMIT
+
+  callSet       = Map.keysSet . Map.filter (== 1) . Map.unionsWith (+) $ map snd callTrees
+  bindSet       = Map.keysSet . Map.filter (< bindSequenceLimit) $ mconcat bindList
+  candidateSet  = mconcat [bindSet `Set.intersection` leafSet, callSet]
+  defCallTree   = Map.fromList callTrees
+  leafSet       = Set.fromList [name | (name, callMap) <- callTrees, Map.null callMap]
+
+  -- keep only the leaves of the candidate call tree
+  inlineSet     = Set.delete "grinMain" $ Data.Foldable.foldr stripCallers candidateSet candidateSet
+
+  -- remove intermediate nodes from the call tree
+  stripCallers name set = set Set.\\ (Map.keysSet $ Map.findWithDefault mempty name defCallTree)
+
+
+  folder :: ExpF Stat -> Stat
+  folder = \case
+    EBindF left _ right
+      -> mconcat [left, right, Stat 1 mempty]
+
+    SAppF name _
+      | not (isExternalName exts name)
+      -> Stat 0 $ Map.singleton name 1
+
+    exp -> Data.Foldable.fold exp
+
+-- transformation
+
+-- TODO: add the cloned variables to the type env
+-- QUESTION: apo OR ana ???
+inlining :: Set Name -> TypeEnv -> Program -> (Program, ExpChanges)
+inlining functionsToInline typeEnv prog@(Program exts defs) = evalNameM prog $ apoM builder prog where
+
+  defMap :: Map Name Def
+  defMap = Map.fromList [(name, def) | def@(Def name _ _) <- defs]
+
+  builder :: Exp -> NameM (ExpF (Either Exp Exp))
+  builder = \case
+
+    -- HINT: do not touch functions marked to inline
+    Def name args body | Set.member name functionsToInline -> pure . DefF name args $ Left body
+
+    -- HINT: bind argument values to function's new arguments and append the body with the fresh names
+    --       with this solution the name refreshing is just a name mapping and does not require a substitution map
+    SApp name args
+      | Set.member name functionsToInline
+      , Just def <- Map.lookup name defMap
+      -> do
+        freshDef <- refreshNames mempty def
+        let (Def _ argNames funBody, nameMap) = freshDef
+        let bind (n,v) e = EBind (SReturn v) (VarPat n) e
+        pure . SBlockF . Left $ foldr bind funBody . zip argNames . map Var $ args
+
+    exp -> pure (Right <$> project exp)
+
+{-
+  - maintain type env
+  - test inlining
+  - test inline selection
+  - test inline: autoselection + inlining
+
+-}
+
+lateInlining :: TypeEnv -> Exp -> (Exp, ExpChanges)
+lateInlining typeEnv prog = first (cleanup nameSet typeEnv) $ inlining nameSet typeEnv prog where
+  nameSet = selectInlineSet prog
+
+inlineEval :: TypeEnv -> Exp -> (Exp, ExpChanges)
+inlineEval te = first (cleanup nameSet te) . inlining nameSet te where
+  nameSet = Set.fromList ["eval", "idr_{EVAL_0}"]
+
+inlineApply :: TypeEnv -> Exp -> (Exp, ExpChanges)
+inlineApply te = first (cleanup nameSet te) . inlining nameSet te where
+  nameSet = Set.fromList ["apply", "idr_{APPLY_0}"]
+
+inlineBuiltins :: TypeEnv -> Exp -> (Exp, ExpChanges)
+inlineBuiltins te = first (cleanup nameSet te) . inlining nameSet te where
+  nameSet = Set.fromList ["_rts_int_gt", "_rts_int_add", "_rts_int_print"] -- TODO: use proper selection
+
+cleanup :: Set Name -> TypeEnv -> Program -> Program
+cleanup nameSet typeEnv (Program exts defs) =
+  Program exts [def | def@(Def name _ _) <- defs, Set.notMember name nameSet]
diff --git a/grin/test/Transformations/ExtendedSyntax/Optimising/InliningSpec.hs b/grin/test/Transformations/ExtendedSyntax/Optimising/InliningSpec.hs
new file mode 100644
index 00000000..c611fe43
--- /dev/null
+++ b/grin/test/Transformations/ExtendedSyntax/Optimising/InliningSpec.hs
@@ -0,0 +1,59 @@
+{-# LANGUAGE OverloadedStrings, QuasiQuotes, ViewPatterns #-}
+module Transformations.ExtendedSyntax.Optimising.InliningSpec where
+
+import Transformations.ExtendedSyntax.Optimising.Inlining
+
+import qualified Data.Set as Set
+
+import Test.Hspec
+import Test.ExtendedSyntax.Assertions
+import Grin.ExtendedSyntax.TH
+import Grin.ExtendedSyntax.TypeCheck
+import Transformations.ExtendedSyntax.Names (ExpChanges(..))
+
+
+runTests :: IO ()
+runTests = hspec spec
+
+spec :: Spec
+spec = do
+  it "base case" $ do
+    let before = [prog|
+        grinMain =
+          k <- pure 0
+          x <- funA k
+          y <- funA k
+          pure x
+
+        funA i = pure i
+      |]
+    let after = [prog|
+        grinMain =
+          k <- pure 0
+          x <- do
+            i.0 <- pure k
+            pure i.0
+          y <- do
+            i.1 <- pure k
+            pure i.1
+          pure x
+
+        funA i = pure i
+      |]
+    let inlineSet = Set.fromList ["funA"]
+    inlining inlineSet (inferTypeEnv before) before `sameAs` (after, NewNames)
+
+  it "no-inline grinMain" $ do
+    let before = [prog|
+        grinMain =
+          k <- pure 0
+          x <- pure k
+          pure x
+      |]
+    let after = [prog|
+        grinMain =
+          k <- pure 0
+          x <- pure k
+          pure x
+      |]
+    lateInlining (inferTypeEnv before) before `sameAs` (after, NoChange)