diff --git a/CHANGELOG.md b/CHANGELOG.md
--- a/CHANGELOG.md
+++ b/CHANGELOG.md
@@ -1,3 +1,8 @@
+## MMark 0.0.5.6
+
+* Now `blockTrans` and `inlineTrans` are applied to deeply nested elements
+  too, not only top-level elements.
+
 ## MMark 0.0.5.5
 
 * Fixed the bug in parser which signalled a parse error when YAML block was
diff --git a/README.md b/README.md
--- a/README.md
+++ b/README.md
@@ -42,7 +42,7 @@
 ## Quick start: MMark vs GitHub-flavored markdown
 
 It's easy to start using MMark if you're used to GitHub-flavored markdown.
-There are three main differences:
+There are four main differences:
 
 1. URIs are not automatically recognized, you must enclose them in `<` and
    `>`.
diff --git a/Text/MMark/Extension.hs b/Text/MMark/Extension.hs
--- a/Text/MMark/Extension.hs
+++ b/Text/MMark/Extension.hs
@@ -106,7 +106,11 @@
 import qualified Control.Foldl as L
 
 -- | Create an extension that performs a transformation on 'Block's of
--- markdown document.
+-- markdown document. Since a block may contain other blocks we choose to
+-- perform transformations from the most deeply nested blocks moving
+-- upwards. This has the benefit that the result of any transformation is
+-- final in the sense that sub-elements of resulting block won't be
+-- traversed again.
 
 blockTrans :: (Bni -> Bni) -> Extension
 blockTrans f = mempty { extBlockTrans = Endo f }
@@ -131,7 +135,9 @@
 blockRender f = mempty { extBlockRender = Render f }
 
 -- | Create an extension that performs a transformation on 'Inline'
--- components in entire markdown document.
+-- components in entire markdown document. Similarly to 'blockTrans' the
+-- transformation is applied from the most deeply nested elements moving
+-- upwards.
 
 inlineTrans :: (Inline -> Inline) -> Extension
 inlineTrans f = mempty { extInlineTrans = Endo f }
diff --git a/Text/MMark/Render.hs b/Text/MMark/Render.hs
--- a/Text/MMark/Render.hs
+++ b/Text/MMark/Render.hs
@@ -22,9 +22,9 @@
 import Data.Char (isSpace)
 import Data.Function (fix)
 import Data.List.NonEmpty (NonEmpty (..))
-import Data.Monoid hiding ((<>))
 import Data.Semigroup
 import Lucid
+import Text.MMark.Trans
 import Text.MMark.Type
 import Text.MMark.Util
 import qualified Data.List.NonEmpty as NE
@@ -46,10 +46,10 @@
     rBlock
       = applyBlockRender extBlockRender
       . fmap rInlines
-      . appEndo extBlockTrans
+      . applyBlockTrans extBlockTrans
     rInlines
       = (mkOisInternal &&& mapM_ (applyInlineRender extInlineRender))
-      . fmap (appEndo extInlineTrans)
+      . fmap (applyInlineTrans extInlineTrans)
 
 -- | Apply a 'Render' to a given @'Block' 'Html' ()@.
 
diff --git a/Text/MMark/Trans.hs b/Text/MMark/Trans.hs
new file mode 100644
--- /dev/null
+++ b/Text/MMark/Trans.hs
@@ -0,0 +1,47 @@
+-- |
+-- Module      :  Text.MMark.Trans
+-- Copyright   :  © 2017–2018 Mark Karpov
+-- License     :  BSD 3 clause
+--
+-- Maintainer  :  Mark Karpov <markkarpov92@gmail.com>
+-- Stability   :  experimental
+-- Portability :  portable
+--
+-- MMark block\/inline transformation helpers.
+
+{-# LANGUAGE LambdaCase #-}
+
+module Text.MMark.Trans
+  ( applyBlockTrans
+  , applyInlineTrans )
+where
+
+import Data.Monoid hiding ((<>))
+import Text.MMark.Type
+
+-- | Apply block transformation in the @'Endo' 'Bni'@ form to a block 'Bni'.
+
+applyBlockTrans :: Endo Bni -> Bni -> Bni
+applyBlockTrans trans@(Endo f) = \case
+  Blockquote    xs -> f (Blockquote (s xs))
+  OrderedList w xs -> f (OrderedList w (s <$> xs))
+  UnorderedList xs -> f (UnorderedList (s <$> xs))
+  other            -> f other
+  where
+    s = fmap (applyBlockTrans trans)
+
+-- | Apply inline transformation in the @'Endo' 'Inline'@ form to an
+-- 'Inline'.
+
+applyInlineTrans :: Endo Inline -> Inline -> Inline
+applyInlineTrans trans@(Endo f) = \case
+  Emphasis     xs -> f (Emphasis    (s xs))
+  Strong       xs -> f (Strong      (s xs))
+  Strikeout    xs -> f (Strikeout   (s xs))
+  Subscript    xs -> f (Subscript   (s xs))
+  Superscript  xs -> f (Superscript (s xs))
+  Link  xs uri mt -> f (Link  (s xs) uri mt)
+  Image xs uri mt -> f (Image (s xs) uri mt)
+  other           -> f other
+  where
+    s = fmap (applyInlineTrans trans)
diff --git a/Text/MMark/Type.hs b/Text/MMark/Type.hs
--- a/Text/MMark/Type.hs
+++ b/Text/MMark/Type.hs
@@ -121,7 +121,7 @@
   { runRender :: (a -> Html ()) -> a -> Html () }
 
 instance Semigroup (Render a) where
-  Render f <> Render g = Render $ \h -> f (g h)
+  Render f <> Render g = Render (f . g)
 
 instance Monoid (Render a) where
   mempty  = Render id
@@ -221,7 +221,7 @@
 
 instance NFData Inline
 
--- | A wrapper for “originial inlines”. Source inlines are wrapped in this
+-- | A wrapper for “original inlines”. Source inlines are wrapped in this
 -- during rendering of inline components and then it's available to block
 -- render, but only for inspection. Altering of 'Ois' is not possible
 -- because the user cannot construct a value of the 'Ois' type, he\/she can
diff --git a/mmark.cabal b/mmark.cabal
--- a/mmark.cabal
+++ b/mmark.cabal
@@ -1,5 +1,5 @@
 name:                 mmark
-version:              0.0.5.5
+version:              0.0.5.6
 cabal-version:        >= 1.18
 tested-with:          GHC==7.10.3, GHC==8.0.2, GHC==8.2.2
 license:              BSD3
@@ -27,7 +27,7 @@
   default:            False
 
 library
-  build-depends:      aeson            >= 0.11 && < 1.3
+  build-depends:      aeson            >= 0.11 && < 1.4
                     , base             >= 4.8  && < 5.0
                     , case-insensitive >= 1.2  && < 1.3
                     , containers       >= 0.5  && < 0.6
@@ -61,6 +61,7 @@
                     , Text.MMark.Parser.Internal
                     , Text.MMark.Parser.Internal.Type
                     , Text.MMark.Render
+                    , Text.MMark.Trans
                     , Text.MMark.Type
                     , Text.MMark.Util
   if flag(dev)
@@ -74,7 +75,7 @@
   hs-source-dirs:     tests
   type:               exitcode-stdio-1.0
   build-depends:      QuickCheck       >= 2.4  && < 3.0
-                    , aeson            >= 0.11 && < 1.3
+                    , aeson            >= 0.11 && < 1.4
                     , base             >= 4.8  && < 5.0
                     , foldl            >= 1.2  && < 1.4
                     , hspec            >= 2.0  && < 3.0
@@ -100,7 +101,7 @@
   hs-source-dirs:     bench/speed
   type:               exitcode-stdio-1.0
   build-depends:      base             >= 4.8 && < 5.0
-                    , criterion        >= 0.6.2.1 && < 1.4
+                    , criterion        >= 0.6.2.1 && < 1.5
                     , mmark
                     , text             >= 0.2 && < 1.3
   if flag(dev)
diff --git a/tests/Text/MMark/ExtensionSpec.hs b/tests/Text/MMark/ExtensionSpec.hs
--- a/tests/Text/MMark/ExtensionSpec.hs
+++ b/tests/Text/MMark/ExtensionSpec.hs
@@ -19,11 +19,15 @@
 
 spec :: Spec
 spec = parallel $ do
-  describe "blockTrans" $
+  describe "blockTrans" $ do
     it "works" $ do
       doc <- mkDoc "# My heading"
       toText (MMark.useExtension h1_to_h2 doc)
         `shouldBe` "<h2 id=\"my-heading\">My heading</h2>\n"
+    it "extensions can affect nested block structures" $ do
+      doc <- mkDoc "* # My heading"
+      toText (MMark.useExtension h1_to_h2 doc)
+        `shouldBe` "<ul>\n<li>\n<h2 id=\"my-heading\">My heading</h2>\n</li>\n</ul>\n"
   describe "blockRender" $ do
     it "works" $ do
       doc <- mkDoc "# My heading"
@@ -33,11 +37,15 @@
       doc <- mkDoc "* # Something"
       toText (MMark.useExtension add_h1_content doc)
        `shouldBe` "<ul>\n<li>\n<h1 data-content=\"Something\" id=\"something\">Something</h1>\n</li>\n</ul>\n"
-  describe "inlineTrans" $
+  describe "inlineTrans" $ do
     it "works" $ do
       doc <- mkDoc "# My *heading*"
       toText (MMark.useExtension em_to_strong doc)
         `shouldBe` "<h1 id=\"my-heading\">My <strong>heading</strong></h1>\n"
+    it "extensions can affect nested inline structures" $ do
+      doc <- mkDoc "# My ~*heading*~"
+      toText (MMark.useExtension em_to_strong doc)
+        `shouldBe` "<h1 id=\"my-heading\">My <sub><strong>heading</strong></sub></h1>\n"
   describe "inlineRender" $ do
     it "works" $ do
       doc <- mkDoc "# My *heading*"
@@ -134,7 +142,7 @@
       [ L.data_ "content" (Ext.asPlainText . Ext.getOis . fst $ inner) ]
     other          -> old other
 
--- | Covert all 'Emphasis' to 'Strong'.
+-- | Convert all 'Emphasis' to 'Strong'.
 
 em_to_strong :: MMark.Extension
 em_to_strong = Ext.inlineTrans $ \case