diff --git a/data/init.lua b/data/init.lua
new file mode 100644
index 000000000..7a46269d8
--- /dev/null
+++ b/data/init.lua
@@ -0,0 +1,6 @@
+-- This Lua script is run every time the Lua interpreter is started when running
+-- a Lua filter. It can be customized to load additional modules or to alter the
+-- default modules.
+
+pandoc = require 'pandoc'
+pandoc.mediabag = require 'pandoc.mediabag'
diff --git a/doc/lua-filters.md b/doc/lua-filters.md
index 11643da84..9beeda185 100644
--- a/doc/lua-filters.md
+++ b/doc/lua-filters.md
@@ -3,7 +3,7 @@ title: Pandoc Lua Filters
 author:
 - Albert Krewinkel
 - John MacFarlane
-date: 'November 20, 2017'
+date: 'December 6, 2017'
 ---
 
 # Introduction
@@ -176,6 +176,34 @@ Some pandoc functions have been made available in lua:
   which stores binary content such as images that may be
   included in the final document.
 
+# Lua interpreter initialization
+
+The way the Lua interpreter is set-up can be controlled by
+placing a file `init.lua` in pandoc's data directory. The
+default init file loads the `pandoc` and `pandoc.mediabag`
+modules:
+
+``` lua
+pandoc = require 'pandoc'
+pandoc.mediabag = require 'pandoc.mediabag'
+```
+
+A common use-case would be to add code to load additional
+modules or to alter default modules. E.g., the following snippet
+adds all unicode-aware functions defined in the [`text`
+module](#module-text) to the default `string` module, prefixed
+with the string `uc_`.
+
+```lua
+for name, fn in pairs(require 'text') do
+  string['uc_' .. name] = fn
+end
+```
+
+This makes it possible to apply these functions on strings using
+colon syntax (`mystring:uc_upper()`).
+
+
 # Examples
 
 ## Macro substitution.
diff --git a/pandoc.cabal b/pandoc.cabal
index 2e6f0b339..e3912d89c 100644
--- a/pandoc.cabal
+++ b/pandoc.cabal
@@ -108,6 +108,8 @@ data-files:
                  data/abbreviations
                  -- sample lua custom writer
                  data/sample.lua
+                 -- lua init script
+                 data/init.lua
                  -- pandoc lua module
                  data/pandoc.lua
                  -- lua List module
diff --git a/src/Text/Pandoc/Lua.hs b/src/Text/Pandoc/Lua.hs
index 1ca67dced..7132ad718 100644
--- a/src/Text/Pandoc/Lua.hs
+++ b/src/Text/Pandoc/Lua.hs
@@ -48,10 +48,11 @@ import Foreign.Lua (FromLuaStack (peek), Lua, LuaException (..),
                     Status (OK), ToLuaStack (push))
 import Text.Pandoc.Class (PandocIO, getCommonState, getMediaBag, setMediaBag)
 import Text.Pandoc.Definition
+import Text.Pandoc.Lua.Filter (LuaFilter, walkMWithLuaFilter)
 import Text.Pandoc.Lua.Packages (LuaPackageParams (..),
                                  installPandocPackageSearcher)
-import Text.Pandoc.Lua.PandocModule (pushMediaBagModule, pushPandocModule)
-import Text.Pandoc.Lua.Filter (LuaFilter, walkMWithLuaFilter)
+import Text.Pandoc.Lua.PandocModule (pushPandocModule) -- TODO: remove
+import Text.Pandoc.Lua.Util (loadScriptFromDataDir)
 import qualified Foreign.Lua as Lua
 import qualified Foreign.Lua.Module.Text as Lua
 
@@ -101,17 +102,11 @@ luaPackageParams datadir = do
 
 -- Initialize the lua state with all required values
 initLuaState :: LuaPackageParams -> Lua ()
-initLuaState luaPkgParams@(LuaPackageParams commonState datadir mbRef) = do
+initLuaState luaPkgParams = do
   Lua.openlibs
   Lua.preloadTextModule "text"
   installPandocPackageSearcher luaPkgParams
-  pushPandocModule datadir
-  -- add MediaBag module
-  push "mediabag"
-  pushMediaBagModule commonState mbRef
-  Lua.rawset (-3)
-  Lua.setglobal "pandoc"
-  return ()
+  loadScriptFromDataDir (luaPkgDataDir luaPkgParams) "init.lua"
 
 pushGlobalFilter :: Lua ()
 pushGlobalFilter = do
diff --git a/src/Text/Pandoc/Lua/PandocModule.hs b/src/Text/Pandoc/Lua/PandocModule.hs
index 744edfe82..75f884c46 100644
--- a/src/Text/Pandoc/Lua/PandocModule.hs
+++ b/src/Text/Pandoc/Lua/PandocModule.hs
@@ -60,7 +60,7 @@ import qualified Text.Pandoc.MediaBag as MB
 
 -- | Push the "pandoc" on the lua stack. Requires the `list` module to be
 -- loaded.
-pushPandocModule :: Maybe FilePath -> Lua ()
+pushPandocModule :: Maybe FilePath -> Lua NumResults
 pushPandocModule datadir = do
   loadScriptFromDataDir datadir "pandoc.lua"
   addFunction "_pipe" pipeFn
@@ -68,6 +68,7 @@ pushPandocModule datadir = do
   addFunction "sha1" sha1HashFn
   addFunction "walk_block" walkBlock
   addFunction "walk_inline" walkInline
+  return 1
 
 walkElement :: (ToLuaStack a, Walkable [Inline] a, Walkable [Block] a)
             => a -> LuaFilter -> Lua NumResults
@@ -99,14 +100,14 @@ readDoc formatSpec content = do
 --
 -- MediaBag submodule
 --
-pushMediaBagModule :: CommonState -> IORef MB.MediaBag -> Lua ()
+pushMediaBagModule :: CommonState -> IORef MB.MediaBag -> Lua NumResults
 pushMediaBagModule commonState mediaBagRef = do
   Lua.newtable
   addFunction "insert" (insertMediaFn mediaBagRef)
   addFunction "lookup" (lookupMediaFn mediaBagRef)
   addFunction "list" (mediaDirectoryFn mediaBagRef)
   addFunction "fetch" (fetch commonState mediaBagRef)
-  return ()
+  return 1
 
 addFunction :: ToHaskellFunction a => String -> a -> Lua ()
 addFunction name fn = do