diff --git a/mongomap/base.py b/mongomap/base.py
new file mode 100644
index 00000000..b6542d8a
--- /dev/null
+++ b/mongomap/base.py
@@ -0,0 +1,101 @@
+
+class ValidationError(Exception):
+    pass
+
+
+class BaseField(object):
+    """A base class for fields in a MongoDB document. Instances of this class
+    may be added to subclasses of `Document` to define a document's schema.
+    """
+    
+    def __init__(self, name=None, default=None):
+        self.name = name
+        self.default = default
+
+    def __get__(self, instance, owner):
+        """Descriptor for retrieving a value from a field in a document. Do 
+        any necessary conversion between Python and MongoDB types.
+        """
+        if instance is None:
+            # Document class being used rather than a document object
+            return self
+
+        # Get value from document instance if available, if not use default
+        value = instance._data.get(self.name)
+        if value is not None:
+            value = self._to_python(value)
+        elif self.default is not None:
+            value = self.default
+            if callable(value):
+                value = value()
+        return value
+
+    def __set__(self, instance, value):
+        """Descriptor for assigning a value to a field in a document. Do any 
+        necessary conversion between Python and MongoDB types.
+        """
+        if value is not None:
+            try:
+                value = self._to_python(value)
+                self._validate(value)
+                value = self._to_mongo(value)
+            except ValueError:
+                raise ValidationError('Invalid value for field of type "' +
+                                      self.__class__.__name__ + '"')
+        instance._data[self.name] = value
+
+    def _to_python(self, value):
+        """Convert a MongoDB-compatible type to a Python type.
+        """
+        return unicode(value)
+
+    def _to_mongo(self, value):
+        """Convert a Python type to a MongoDB-compatible type.
+        """
+        return self._to_python(value)
+
+    def _validate(self, value):
+        """Perform validation on a value.
+        """
+        return value
+
+
+class DocumentMetaclass(type):
+    """Metaclass for all documents.
+    """
+
+    def __new__(cls, name, bases, attrs):
+        doc_fields = {}
+
+        # Include all fields present in superclasses
+        for base in bases:
+            if hasattr(base, '_fields'):
+                doc_fields.update(base._fields)
+
+        # Add the document's fields to the _fields attribute
+        for attr_name, attr_val in attrs.items():
+            if issubclass(attr_val.__class__, BaseField):
+                if not attr_val.name:
+                    attr_val.name = attr_name
+                doc_fields[attr_name] = attr_val
+        attrs['_fields'] = doc_fields
+
+        return type.__new__(cls, name, bases, attrs)
+
+
+class BaseDocument(object):
+
+    def __init__(self, **values):
+        self._data = {}
+        # Assign initial values to instance
+        for attr_name, attr_value in self._fields.items():
+            if attr_name in values:
+                setattr(self, attr_name, values.pop(attr_name))
+            else:
+                # Use default value
+                setattr(self, attr_name, getattr(self, attr_name))
+
+    def __iter__(self):
+        # Use _data rather than _fields as iterator only looks at names so
+        # values don't need to be converted to Python types
+        return iter(self._data)
diff --git a/mongomap/document.py b/mongomap/document.py
index 2fed2be6..96d43003 100644
--- a/mongomap/document.py
+++ b/mongomap/document.py
@@ -1,29 +1,6 @@
-import pymongo
-
-import fields
-
-class DocumentMetaclass(type):
-    """Metaclass for all documents.
-    """
-
-    def __new__(cls, name, bases, attrs):
-        doc_fields = {}
-
-        # Include all fields present in superclasses
-        for base in bases:
-            if hasattr(base, '_fields'):
-                doc_fields.update(base._fields)
-
-        # Add the document's fields to the _fields attribute
-        for attr_name, attr_val in attrs.items():
-            if issubclass(attr_val.__class__, fields.Field):
-                if not attr_val.name:
-                    attr_val.name = attr_name
-                doc_fields[attr_name] = attr_val
-        attrs['_fields'] = doc_fields
-
-        return type.__new__(cls, name, bases, attrs)
+from base import DocumentMetaclass, BaseDocument
 
+#import pymongo
 
 class TopLevelDocumentMetaclass(DocumentMetaclass):
     """Metaclass for top-level documents (i.e. documents that have their own
@@ -48,21 +25,12 @@ class TopLevelDocumentMetaclass(DocumentMetaclass):
         return DocumentMetaclass.__new__(cls, name, bases, attrs)
 
 
-class Document(object):
+class EmbeddedDocument(BaseDocument):
+    
+    __metaclass__ = DocumentMetaclass
+
+
+class Document(BaseDocument):
 
     __metaclass__ = TopLevelDocumentMetaclass
 
-    def __init__(self, **values):
-        self._data = {}
-        # Assign initial values to instance
-        for attr_name, attr_value in self._fields.items():
-            if attr_name in values:
-                setattr(self, attr_name, values.pop(attr_name))
-            else:
-                # Use default value
-                setattr(self, attr_name, getattr(self, attr_name))
-
-    def __iter__(self):
-        # Use _data rather than _fields as iterator only looks at names so
-        # values don't need to be converted to Python types
-        return iter(self._data)
diff --git a/mongomap/fields.py b/mongomap/fields.py
index 928fe5ce..f642f80c 100644
--- a/mongomap/fields.py
+++ b/mongomap/fields.py
@@ -1,85 +1,20 @@
+from base import BaseField, ValidationError
+from document import EmbeddedDocument
+ 
 import re
 
 
 __all__ = ['StringField', 'IntField', 'ValidationError']
 
 
-class ValidationError(Exception):
-    pass
-
-
-class Field(object):
-    """A base class for fields in a MongoDB document. Instances of this class
-    may be added to subclasses of `Document` to define a document's schema.
-    """
-    
-    def __init__(self, name=None, default=None):
-        self.name = name
-        self.default = default
-
-    def __get__(self, instance, owner):
-        """Descriptor for retrieving a value from a field in a document. Do 
-        any necessary conversion between Python and MongoDB types.
-        """
-        if instance is None:
-            # Document class being used rather than a document object
-            return self
-
-        # Get value from document instance if available, if not use default
-        value = instance._data.get(self.name)
-        if value is not None:
-            value = self._to_python(value)
-        elif self.default is not None:
-            value = self.default
-            if callable(value):
-                value = value()
-        return value
-
-    def __set__(self, instance, value):
-        """Descriptor for assigning a value to a field in a document. Do any 
-        necessary conversion between Python and MongoDB types.
-        """
-        if value is not None:
-            try:
-                value = self._to_python(value)
-                self._validate(value)
-                value = self._to_mongo(value)
-            except ValueError:
-                raise ValidationError('Invalid value for field of type "' +
-                                      self.__class__.__name__ + '"')
-        instance._data[self.name] = value
-
-    def _to_python(self, value):
-        """Convert a MongoDB-compatible type to a Python type.
-        """
-        return unicode(value)
-
-    def _to_mongo(self, value):
-        """Convert a Python type to a MongoDB-compatible type.
-        """
-        return self._to_python(value)
-
-    def _validate(self, value):
-        """Perform validation on a value.
-        """
-        return value
-
-
-class NestedDocumentField(Field):
-    """A nested document field. Only valid values are subclasses of 
-    NestedDocument. 
-    """
-    pass
-
-
-class StringField(Field):
+class StringField(BaseField):
     """A unicode string field.
     """
     
     def __init__(self, regex=None, max_length=None, **kwargs):
         self.regex = re.compile(regex) if regex else None
         self.max_length = max_length
-        Field.__init__(self, **kwargs)
+        BaseField.__init__(self, **kwargs)
 
     def _validate(self, value):
         if self.max_length is not None and len(value) > self.max_length:
@@ -90,13 +25,13 @@ class StringField(Field):
             raise ValidationError(message)
 
 
-class IntField(Field):
+class IntField(BaseField):
     """An integer field.
     """
 
     def __init__(self, min_value=None, max_value=None, **kwargs):
         self.min_value, self.max_value = min_value, max_value
-        Field.__init__(self, **kwargs)
+        BaseField.__init__(self, **kwargs)
     
     def _to_python(self, value):
         return int(value)
@@ -107,3 +42,10 @@ class IntField(Field):
 
         if self.max_value is not None and value > self.max_value:
             raise ValidationError('Integer value is too large')
+
+
+class EmbeddedDocumentField(BaseField):
+    """An embedded document field. Only valid values are subclasses of 
+    EmbeddedDocument. 
+    """
+    pass