diff --git a/rest_framework/fields.py b/rest_framework/fields.py
index 6caae9242..cda1748d0 100644
--- a/rest_framework/fields.py
+++ b/rest_framework/fields.py
@@ -256,6 +256,7 @@ class WritableField(Field):
     default_error_messages = {
         'required': _('This field is required.'),
         'invalid': _('Invalid value.'),
+        'missing': _('Related object does not exist.'),
     }
     widget = widgets.TextInput
     default = None
diff --git a/rest_framework/serializers.py b/rest_framework/serializers.py
index 43d339da0..606b115ab 100644
--- a/rest_framework/serializers.py
+++ b/rest_framework/serializers.py
@@ -21,6 +21,7 @@ from django.core.paginator import Page
 from django.db import models
 from django.forms import widgets
 from django.utils.datastructures import SortedDict
+from django.utils.translation import ugettext_lazy as _
 from django.core.exceptions import ObjectDoesNotExist
 from rest_framework.compat import get_concrete_model, six
 from rest_framework.settings import api_settings
@@ -941,6 +942,7 @@ class ModelSerializer(Serializer):
         """
         m2m_data = {}
         related_data = {}
+        related_models_to_save = {}
         nested_forward_relations = {}
         meta = self.opts.model._meta
 
@@ -969,13 +971,33 @@ class ModelSerializer(Serializer):
             if isinstance(self.fields.get(field_name, None), Serializer):
                 nested_forward_relations[field_name] = attrs[field_name]
 
-        # Create an empty instance of the model
+        # Update an existing instance...
         if instance is None:
             instance = self.opts.model()
 
         for key, val in attrs.items():
+            keys = key.split('.')
+
+            # Work on the current instance for this attribute
+            attr_instance = instance
+
+            # Raise an error if we span more than one relation
+            if len(keys) > 2:
+                self._errors[key] = 'Can not span more than a relation.'
+                continue
+
+            # Mark the related instance as the one to save
+            if len(keys) == 2:
+                try:
+                    attr_instance = getattr(instance, keys[0])
+                    related_models_to_save[key] = attr_instance
+                except (AttributeError, ObjectDoesNotExist):
+                    self._errors[key] = self.error_messages['missing']
+                    continue
+
+            # Assign the value
             try:
-                setattr(instance, key, val)
+                setattr(attr_instance, keys[-1], val)
             except ValueError:
                 self._errors[key] = [self.error_messages['required']]
 
@@ -986,6 +1008,7 @@ class ModelSerializer(Serializer):
         instance._related_data = related_data
         instance._m2m_data = m2m_data
         instance._nested_forward_relations = nested_forward_relations
+        instance._related_models_to_save = related_models_to_save
 
         return instance
 
@@ -1044,6 +1067,10 @@ class ModelSerializer(Serializer):
                     setattr(obj, accessor_name, related)
             del(obj._related_data)
 
+        if getattr(obj, '_related_models_to_save', None):
+            for related in obj._related_models_to_save.values():
+                self.save_object(related)
+
 
 class HyperlinkedModelSerializerOptions(ModelSerializerOptions):
     """
diff --git a/rest_framework/tests/test_serializer.py b/rest_framework/tests/test_serializer.py
index fb2eac0ba..e7cbcedbe 100644
--- a/rest_framework/tests/test_serializer.py
+++ b/rest_framework/tests/test_serializer.py
@@ -1974,3 +1974,68 @@ class BoolenFieldTypeTest(TestCase):
         '''
         bfield = self.serializer.get_fields()['started']
         self.assertEqual(type(bfield), fields.BooleanField)
+
+
+class RelationSpanningSerializerTest(TestCase):
+    def test_model_traversal_creation(self):
+        """Update a field through a foreign key during a creation."""
+        class TicketSerializer(serializers.ModelSerializer):
+            username = fields.CharField(source='assigned.name')
+
+            class Meta:
+                model = Ticket
+                fields = ('username',)
+
+        serializer = TicketSerializer(data={'username': 'doe'})
+        self.assertFalse(serializer.is_valid())
+        self.assertEqual(serializer.errors, {'username': 'You can not set dotted sources during creation.'})
+
+    def test_model_traversal_update(self):
+        """Update a field through a foreign key during an update."""
+        class TicketSerializer(serializers.ModelSerializer):
+            username = fields.CharField(source='assigned.name')
+
+            class Meta:
+                model = Ticket
+                fields = ('username',)
+
+        owner = Person.objects.create(name='john')
+        reviewer = Person.objects.create(name='reviewer')
+        ticket = Ticket.objects.create(assigned=owner, reviewer=reviewer)
+        serializer = TicketSerializer(ticket, data={'username': 'doe'})
+        self.assertTrue(serializer.is_valid())
+        self.assertEqual(serializer.object.assigned.name, 'doe')
+        serializer.save()
+        self.assertEqual(Person.objects.get(id=owner.id).name, 'doe')
+
+    def test_failing_model_traversal(self):
+        """Update a field through an unknown relation."""
+        class TicketSerializer(serializers.ModelSerializer):
+            username = fields.CharField(source='demo.name')
+
+            class Meta:
+                model = Ticket
+                fields = ('username',)
+
+        owner = Person(name='john')
+        reviewer = Person(name='reviewer')
+        ticket = Ticket(assigned=owner, reviewer=reviewer)
+        serializer = TicketSerializer(ticket, data={'username': 'doe'})
+        self.assertFalse(serializer.is_valid())
+        self.assertEqual(serializer.errors, {'username': 'Related object does not exist.'})
+
+    def test_multiple_model_traversal_update(self):
+        """Update a field through a foreign key during an update."""
+        class TicketSerializer(serializers.ModelSerializer):
+            username = fields.CharField(source='assigned.demo.name')
+
+            class Meta:
+                model = Ticket
+                fields = ('username',)
+
+        owner = Person.objects.create(name='john')
+        reviewer = Person.objects.create(name='reviewer')
+        ticket = Ticket.objects.create(assigned=owner, reviewer=reviewer)
+        serializer = TicketSerializer(ticket, data={'username': 'doe'})
+        self.assertFalse(serializer.is_valid())
+        self.assertEqual(serializer.errors, {'username': 'Can not span more than a relation.'})