diff --git a/CHANGELOG.md b/CHANGELOG.md
index aab1a10..518b53e 100644
--- a/CHANGELOG.md
+++ b/CHANGELOG.md
@@ -11,9 +11,11 @@ and this project adheres to
 - AST for the GraphQL schema.
 
 ### Changed
-- Rename `AST.Definition` into `AST.ExecutableDefinition`.
-  `AST.TypeSystemDefinition` and `AST.TypeSystemExtension` can also be
-  definitions.
+- Rename `AST.Definition` into `AST.Document.ExecutableDefinition`.
+  `AST.Document.TypeSystemDefinition` and `AST.Document.TypeSystemExtension`
+  can also be definitions.
+- Move all AST data to `AST.Document` and reexport them.
+- Rename `AST.OperationSelectionSet` to `AST.Document.SelectionSet`.
 
 ### Removed
 - `AST.Field`, `AST.InlineFragment` and `AST.FragmentSpread`.
diff --git a/src/Language/GraphQL/AST.hs b/src/Language/GraphQL/AST.hs
index ea7912a..aba6dfd 100644
--- a/src/Language/GraphQL/AST.hs
+++ b/src/Language/GraphQL/AST.hs
@@ -1,157 +1,6 @@
 -- | Target AST for Parser.
 module Language.GraphQL.AST
-    ( Alias
-    , Argument(..)
-    , ExecutableDefinition(..)
-    , Directive(..)
-    , FragmentDefinition(..)
-    , Name
-    , NonNullType(..)
-    , ObjectField(..)
-    , OperationDefinition(..)
-    , OperationType(..)
-    , Selection(..)
-    , SelectionSet
-    , SelectionSetOpt
-    , Type(..)
-    , TypeCondition
-    , Value(..)
-    , VariableDefinition(..)
+    ( module Language.GraphQL.AST.Document
     ) where
 
-import Data.Int (Int32)
-import Data.List.NonEmpty (NonEmpty)
-import Data.Text (Text)
-
--- | Name
-type Name = Text
-
--- | Directive.
-data Directive = Directive Name [Argument] deriving (Eq, Show)
-
--- * Operations
-
--- | Top-level definition of a document, either an operation or a fragment.
-data ExecutableDefinition
-    = DefinitionOperation OperationDefinition
-    | DefinitionFragment FragmentDefinition
-    deriving (Eq, Show)
-
--- | Operation definition.
-data OperationDefinition
-    = OperationSelectionSet SelectionSet
-    | OperationDefinition OperationType
-                          (Maybe Name)
-                          [VariableDefinition]
-                          [Directive]
-                          SelectionSet
-    deriving (Eq, Show)
-
--- | GraphQL has 3 operation types: queries, mutations and subscribtions.
---
--- Currently only queries and mutations are supported.
-data OperationType = Query | Mutation deriving (Eq, Show)
-
--- * Selections
-
--- | "Top-level" selection, selection on an operation or fragment.
-type SelectionSet = NonEmpty Selection
-
--- | Field selection.
-type SelectionSetOpt = [Selection]
-
--- | Single GraphQL field.
---
--- The only required property of a field is its name. Optionally it can also
--- have an alias, arguments or a list of subfields.
---
--- Given the following query:
---
--- @
--- {
---   zuck: user(id: 4) {
---     id
---     name
---   }
--- }
--- @
---
--- * "user", "id" and "name" are field names.
--- * "user" has two subfields, "id" and "name".
--- * "zuck" is an alias for "user". "id" and "name" have no aliases.
--- * "id: 4" is an argument for "user". "id" and "name" don't have any
--- arguments.
-data Selection
-    = Field (Maybe Alias) Name [Argument] [Directive] SelectionSetOpt
-    | FragmentSpread Name [Directive]
-    | InlineFragment (Maybe TypeCondition) [Directive] SelectionSet
-    deriving (Eq, Show)
-
--- | Alternative field name.
---
--- @
--- {
---   smallPic: profilePic(size: 64)
---   bigPic: profilePic(size: 1024)
--- }
--- @
---
--- Here "smallPic" and "bigPic" are aliases for the same field, "profilePic",
--- used to distinquish between profile pictures with different arguments
--- (sizes).
-type Alias = Name
-
--- | Single argument.
---
--- @
--- {
---   user(id: 4) {
---     name
---   }
--- }
--- @
---
---  Here "id" is an argument for the field "user" and its value is 4.
-data Argument = Argument Name Value deriving (Eq,Show)
-
--- | Fragment definition.
-data FragmentDefinition
-    = FragmentDefinition Name TypeCondition [Directive] SelectionSet
-    deriving (Eq, Show)
-
--- * Inputs
-
--- | Input value.
-data Value = Variable Name
-           | Int Int32
-           | Float Double
-           | String Text
-           | Boolean Bool
-           | Null
-           | Enum Name
-           | List [Value]
-           | Object [ObjectField]
-           deriving (Eq, Show)
-
--- | Key-value pair.
---
--- A list of 'ObjectField's represents a GraphQL object type.
-data ObjectField = ObjectField Name Value deriving (Eq, Show)
-
--- | Variable definition.
-data VariableDefinition = VariableDefinition Name Type (Maybe Value)
-                          deriving (Eq, Show)
-
--- | Type condition.
-type TypeCondition = Name
-
--- | Type representation.
-data Type = TypeNamed   Name
-          | TypeList    Type
-          | TypeNonNull NonNullType
-            deriving (Eq, Show)
-
--- | Helper type to represent Non-Null types and lists of such types.
-data NonNullType = NonNullTypeNamed Name
-                 | NonNullTypeList  Type
-                   deriving (Eq, Show)
+import Language.GraphQL.AST.Document
diff --git a/src/Language/GraphQL/AST/Document.hs b/src/Language/GraphQL/AST/Document.hs
index ebe8918..b94b629 100644
--- a/src/Language/GraphQL/AST/Document.hs
+++ b/src/Language/GraphQL/AST/Document.hs
@@ -1,34 +1,46 @@
 -- | This module defines an abstract syntax tree for the @GraphQL@ language. It
---   follows closely the structure given in the specification. Please refer to
---   <https://facebook.github.io/graphql/ Facebook's GraphQL Specification>.
---   for more information.
+-- follows closely the structure given in the specification. Please refer to
+-- <https://facebook.github.io/graphql/ Facebook's GraphQL Specification>.
+-- for more information.
 module Language.GraphQL.AST.Document
-    ( Definition(..)
+    ( Alias
+    , Argument(..)
+    , Definition(ExecutableDefinition)
+    , Directive(..)
     , Document
     , ExecutableDefinition(..)
+    , FragmentDefinition(..)
+    , Name
+    , NonNullType(..)
+    , ObjectField(..)
+    , OperationDefinition(..)
+    , OperationType(..)
+    , Selection(..)
+    , SelectionSet
+    , SelectionSetOpt
+    , Type(..)
+    , TypeCondition
+    , Value(..)
+    , VariableDefinition(..)
     ) where
 
+import Data.Int (Int32)
 import Data.List.NonEmpty (NonEmpty)
 import Data.Text (Text)
-import Language.GraphQL.AST
-    ( ExecutableDefinition(..)
-    , Directive
-    , Name
-    , OperationType
-    , Type
-    , Value
-    )
 import Language.GraphQL.AST.DirectiveLocation
 
 -- * Language
 
+-- ** Source Text
+
+-- | Name.
+type Name = Text
+
 -- ** Document
 
 -- | GraphQL document.
 type Document = NonEmpty Definition
 
-type NamedType = Name
-
 -- | All kinds of definitions that can occur in a GraphQL document.
 data Definition
     = ExecutableDefinition ExecutableDefinition
@@ -36,12 +48,190 @@ data Definition
     | TypeSystemExtension TypeSystemExtension
     deriving (Eq, Show)
 
+-- | Top-level definition of a document, either an operation or a fragment.
+data ExecutableDefinition
+    = DefinitionOperation OperationDefinition
+    | DefinitionFragment FragmentDefinition
+    deriving (Eq, Show)
+
+-- ** Operations
+
+-- | Operation definition.
+data OperationDefinition
+    = SelectionSet SelectionSet
+    | OperationDefinition
+        OperationType
+        (Maybe Name)
+        [VariableDefinition]
+        [Directive]
+        SelectionSet
+    deriving (Eq, Show)
+
+-- | GraphQL has 3 operation types:
+--
+-- * query - a read-only fetch.
+-- * mutation - a write operation followed by a fetch.
+-- * subscription - a long-lived request that fetches data in response to
+-- source events.
+--
+-- Currently only queries and mutations are supported.
+data OperationType = Query | Mutation deriving (Eq, Show)
+
+-- ** Selection Sets
+
+-- | "Top-level" selection, selection on an operation or fragment.
+type SelectionSet = NonEmpty Selection
+
+-- | Field selection.
+type SelectionSetOpt = [Selection]
+
+-- | Selection is a single entry in a selection set. It can be a single field,
+-- fragment spread or inline fragment.
+--
+-- The only required property of a field is its name. Optionally it can also
+-- have an alias, arguments, directives and a list of subfields.
+--
+-- In the following query "user" is a field with two subfields, "id" and "name":
+--
+-- @
+-- {
+--   user {
+--     id
+--     name
+--   }
+-- }
+-- @
+--
+-- A fragment spread refers to a fragment defined outside the operation and is
+-- expanded at the execution time.
+--
+-- @
+-- {
+--   user {
+--     ...userFragment
+--   }
+-- }
+--
+-- fragment userFragment on UserType {
+--   id
+--   name
+-- }
+-- @
+--
+-- Inline fragments are similar but they don't have any name and the type
+-- condition ("on UserType") is optional.
+--
+-- @
+-- {
+--   user {
+--     ... on UserType {
+--       id
+--       name
+--     }
+-- }
+-- @
+data Selection
+    = Field (Maybe Alias) Name [Argument] [Directive] SelectionSetOpt
+    | FragmentSpread Name [Directive]
+    | InlineFragment (Maybe TypeCondition) [Directive] SelectionSet
+    deriving (Eq, Show)
+
+-- ** Arguments
+
+-- | Single argument.
+--
+-- @
+-- {
+--   user(id: 4) {
+--     name
+--   }
+-- }
+-- @
+--
+--  Here "id" is an argument for the field "user" and its value is 4.
+data Argument = Argument Name Value deriving (Eq,Show)
+
+-- ** Field Alias
+
+-- | Alternative field name.
+--
+-- @
+-- {
+--   smallPic: profilePic(size: 64)
+--   bigPic: profilePic(size: 1024)
+-- }
+-- @
+--
+-- Here "smallPic" and "bigPic" are aliases for the same field, "profilePic",
+-- used to distinquish between profile pictures with different arguments
+-- (sizes).
+type Alias = Name
+
+-- ** Fragments
+
+-- | Fragment definition.
+data FragmentDefinition
+    = FragmentDefinition Name TypeCondition [Directive] SelectionSet
+    deriving (Eq, Show)
+
+-- | Type condition.
+type TypeCondition = Name
+
+-- ** Input Values
+
+-- | Input value.
+data Value
+    = Variable Name
+    | Int Int32
+    | Float Double
+    | String Text
+    | Boolean Bool
+    | Null
+    | Enum Name
+    | List [Value]
+    | Object [ObjectField]
+    deriving (Eq, Show)
+
+-- | Key-value pair.
+--
+--   A list of 'ObjectField's represents a GraphQL object type.
+data ObjectField = ObjectField Name Value deriving (Eq, Show)
+
+-- ** Variables
+
+-- | Variable definition.
+data VariableDefinition = VariableDefinition Name Type (Maybe Value)
+    deriving (Eq, Show)
+
+-- ** Type References
+
+-- | Type representation.
+data Type
+    = TypeNamed Name
+    | TypeList Type
+    | TypeNonNull NonNullType
+    deriving (Eq, Show)
+
+type NamedType = Name
+
+-- | Helper type to represent Non-Null types and lists of such types.
+data NonNullType
+    = NonNullTypeNamed Name
+    | NonNullTypeList Type
+    deriving (Eq, Show)
+
+-- ** Directives
+
+-- | Directive.
+data Directive = Directive Name [Argument] deriving (Eq, Show)
+
 -- * Type System
 
 data TypeSystemDefinition
     = SchemaDefinition [Directive] RootOperationTypeDefinitions
     | TypeDefinition TypeDefinition
-    | DirectiveDefinition Description Name ArgumentsDefinition DirectiveLocation
+    | DirectiveDefinition
+        Description Name ArgumentsDefinition DirectiveLocation
     deriving (Eq, Show)
 
 -- ** Type System Extensions
@@ -109,7 +299,8 @@ newtype ImplementsInterfaces = ImplementsInterfaces (NonEmpty NamedType)
 newtype ImplementsInterfacesOpt = ImplementsInterfacesOpt [NamedType]
     deriving (Eq, Show)
 
-data FieldDefinition = FieldDefinition Description Name ArgumentsDefinition Type
+data FieldDefinition
+    = FieldDefinition Description Name ArgumentsDefinition Type
     deriving (Eq, Show)
 
 newtype ArgumentsDefinition = ArgumentsDefinition [InputValueDefinition]
diff --git a/src/Language/GraphQL/AST/Encoder.hs b/src/Language/GraphQL/AST/Encoder.hs
index e33068d..eb865c9 100644
--- a/src/Language/GraphQL/AST/Encoder.hs
+++ b/src/Language/GraphQL/AST/Encoder.hs
@@ -66,7 +66,7 @@ definition formatter x
         = fragmentDefinition formatter fragment
 
 operationDefinition :: Formatter -> Full.OperationDefinition -> Lazy.Text
-operationDefinition formatter (Full.OperationSelectionSet sels)
+operationDefinition formatter (Full.SelectionSet sels)
     = selectionSet formatter sels
 operationDefinition formatter (Full.OperationDefinition Full.Query name vars dirs sels)
     = "query " <> node formatter name vars dirs sels
diff --git a/src/Language/GraphQL/AST/Parser.hs b/src/Language/GraphQL/AST/Parser.hs
index ad2b96d..113b0a4 100644
--- a/src/Language/GraphQL/AST/Parser.hs
+++ b/src/Language/GraphQL/AST/Parser.hs
@@ -25,13 +25,16 @@ definition = DefinitionOperation <$> operationDefinition
          <?> "definition error!"
 
 operationDefinition :: Parser OperationDefinition
-operationDefinition = OperationSelectionSet <$> selectionSet
-                  <|> OperationDefinition   <$> operationType
-                                            <*> optional name
-                                            <*> opt variableDefinitions
-                                            <*> opt directives
-                                            <*> selectionSet
-                  <?> "operationDefinition error"
+operationDefinition = SelectionSet <$> selectionSet
+    <|> operationDefinition'
+    <?> "operationDefinition error"
+  where
+    operationDefinition'
+        = OperationDefinition <$> operationType
+        <*> optional name
+        <*> opt variableDefinitions
+        <*> opt directives
+        <*> selectionSet
 
 operationType :: Parser OperationType
 operationType = Query <$ symbol "query"
diff --git a/src/Language/GraphQL/Execute/Transform.hs b/src/Language/GraphQL/Execute/Transform.hs
index 28b9481..7c2e100 100644
--- a/src/Language/GraphQL/Execute/Transform.hs
+++ b/src/Language/GraphQL/Execute/Transform.hs
@@ -58,13 +58,13 @@ operations operations' = do
     lift . lift $ NonEmpty.nonEmpty coreOperations
 
 operation :: Full.OperationDefinition -> TransformT Core.Operation
-operation (Full.OperationSelectionSet sels) =
-    operation $ Full.OperationDefinition Full.Query mempty mempty mempty sels
+operation (Full.SelectionSet sels)
+    = operation $ Full.OperationDefinition Full.Query mempty mempty mempty sels
 -- TODO: Validate Variable definitions with substituter
-operation (Full.OperationDefinition Full.Query name _vars _dirs sels) =
-    Core.Query name <$> appendSelection sels
-operation (Full.OperationDefinition Full.Mutation name _vars _dirs sels) =
-    Core.Mutation name <$> appendSelection sels
+operation (Full.OperationDefinition Full.Query name _vars _dirs sels)
+    = Core.Query name <$> appendSelection sels
+operation (Full.OperationDefinition Full.Mutation name _vars _dirs sels)
+    = Core.Mutation name <$> appendSelection sels
 
 -- * Selection
 
diff --git a/tests/Language/GraphQL/AST/EncoderSpec.hs b/tests/Language/GraphQL/AST/EncoderSpec.hs
index 619d7e3..00a875c 100644
--- a/tests/Language/GraphQL/AST/EncoderSpec.hs
+++ b/tests/Language/GraphQL/AST/EncoderSpec.hs
@@ -35,8 +35,7 @@ spec = do
         it "indents block strings in arguments" $
             let arguments = [Argument "message" (String "line1\nline2")]
                 field = Field Nothing "field" arguments [] []
-                set = OperationSelectionSet $ pure field
-                operation = DefinitionOperation set
+                operation = DefinitionOperation $ SelectionSet $ pure field
              in definition pretty operation `shouldBe` [r|{
   field(message: """
     line1