diff --git a/sphinx/util/__init__.py b/sphinx/util/__init__.py
index ec48009f4..a434f3a82 100644
--- a/sphinx/util/__init__.py
+++ b/sphinx/util/__init__.py
@@ -19,6 +19,7 @@ import posixpath
 import traceback
 from os import path
 from codecs import open
+from collections import deque
 
 import docutils
 from docutils.utils import relative_path
@@ -297,3 +298,38 @@ def format_exception_cut_frames(x=1):
     res += tbres[-x:]
     res += traceback.format_exception_only(typ, val)
     return ''.join(res)
+
+class PeekableIterator(object):
+    """
+    An iterator which wraps any iterable and makes it possible to peek to see
+    what's the next item.
+    """
+    def __init__(self, iterable):
+        self.remaining = deque()
+        self._iterator = iter(iterable)
+
+    def __iter__(self):
+        return self
+
+    def next(self):
+        """
+        Returns the next item from the iterator.
+        """
+        if self.remaining:
+            return self.remaining.popleft()
+        return self._iterator.next()
+
+    def push(self, item):
+        """
+        Pushes the `item` on the internal stack, it will be returned on the
+        next :meth:`next` call.
+        """
+        self.remaining.append(item)
+
+    def peek(self):
+        """
+        Returns the next item without changing the state of the iterator.
+        """
+        item = self.next()
+        self.push(item)
+        return item
diff --git a/sphinx/versioning.py b/sphinx/versioning.py
new file mode 100644
index 000000000..42b8bd515
--- /dev/null
+++ b/sphinx/versioning.py
@@ -0,0 +1,144 @@
+# -*- coding: utf-8 -*-
+"""
+    sphinx.versioning
+    ~~~~~~~~~~~~~~~~~
+
+    Implements the low-level algorithms Sphinx uses for the versioning of
+    doctrees.
+
+    :copyright: Copyright 2007-2010 by the Sphinx team, see AUTHORS.
+    :license: BSD, see LICENSE for details.
+"""
+from uuid import uuid4
+from itertools import izip_longest, product
+from difflib import SequenceMatcher
+
+from sphinx.util import PeekableIterator
+
+def add_uids(doctree, condition):
+    """
+    Adds a unique id to every node in the `doctree` which matches the condition
+    and yields it.
+
+    :param doctree:
+        A :class:`docutils.nodes.document` instance.
+
+    :param condition:
+        A callable which returns either ``True`` or ``False`` for a given node.
+    """
+    for node in doctree.traverse(condition):
+        node.uid = uuid4().hex
+        yield node
+
+def merge_node(old, new):
+    """
+    Merges the `old` node with the `new` one, if it's successful the `new` node
+    get's the unique identifier of the `new` one and ``True`` is returned. If
+    the merge is unsuccesful ``False`` is returned.
+    """
+    equals, changed, replaced = make_diff(old.rawsource,
+                                          new.rawsource)
+    if equals or changed:
+        new.uid = old.uid
+        return True
+    return False
+
+def merge_doctrees(old, new, condition):
+    """
+    Merges the `old` doctree with the `new` one while looking at nodes matching
+    the `condition`.
+
+    Each node which replaces another one or has been added to the `new` doctree
+    will be yielded.
+
+    :param condition:
+        A callable which returns either ``True`` or ``False`` for a given node.
+    """
+    old_iter = PeekableIterator(old.traverse(condition))
+    new_iter = PeekableIterator(new.traverse(condition))
+    old_nodes = []
+    new_nodes = []
+    for old_node, new_node in izip_longest(old_iter, new_iter):
+        if old_node is None:
+            new_nodes.append(new_node)
+            continue
+        if new_node is None:
+            old_nodes.append(old_node)
+            continue
+        if not merge_node(old_node, new_node):
+            if old_nodes:
+                for i, very_old_node in enumerate(old_nodes):
+                    if merge_node(very_old_node, new_node):
+                        del old_nodes[i]
+                        # If the last identified node which has not matched the
+                        # unidentified node matches the current one, we have to
+                        # assume that the last unidentified one has been
+                        # inserted.
+                        #
+                        # As the required time multiplies with each insert, we
+                        # want to avoid that by checking if the next
+                        # unidentified node matches the current identified one
+                        # and if so we make a shift.
+                        if i == len(old_nodes):
+                            next_new_node = new_iter.next()
+                            if not merge_node(old_node, next_new_node):
+                                new_iter.push(next_new_node)
+                        break
+            else:
+                old_nodes.append(old_node)
+                new_nodes.append(new_node)
+    for (i, new_node), (j, old_node) in product(enumerate(new_nodes),
+                                                enumerate(old_nodes)):
+        if merge_node(old_node, new_node):
+            del new_nodes[i]
+            del old_nodes[j]
+    for node in new_nodes:
+        node.uid = uuid4().hex
+        # Yielding the new nodes here makes it possible to use this generator
+        # like add_uids
+        yield node
+
+def make_diff(old, new):
+    """
+    Takes two strings `old` and `new` and returns a :class:`tuple` of boolean
+    values ``(equals, changed, replaced)``.
+
+    equals
+
+        ``True`` if the `old` string and the `new` one are equal.
+
+    changed
+
+        ``True`` if the `new` string is a changed version of the `old` one.
+
+    replaced
+
+        ``True`` if the `new` string and the `old` string are totally
+        different.
+
+    .. note:: This assumes the two strings are human readable text or at least
+              something very similar to that, otherwise it can not detect if
+              the string has been changed or replaced. In any case the
+              detection should not be considered reliable.
+    """
+    if old == new:
+        return True, False, False
+    if new in old or levenshtein_distance(old, new) / (len(old) / 100.0) < 70:
+        return False, True, False
+    return False, False, True
+
+def levenshtein_distance(a, b):
+    if len(a) < len(b):
+        a, b = b, a
+    if not a:
+        return len(b)
+    previous_row = xrange(len(b) + 1)
+    for i, column1 in enumerate(a):
+        current_row = [i + 1]
+        for j, column2 in enumerate(b):
+            insertions = previous_row[j + 1] + 1
+            deletions = current_row[j] + 1
+            substitutions = previous_row[j] + (column1 != column2)
+            current_row.append(min(insertions, deletions, substitutions))
+        previous_row = current_row
+    return previous_row[-1]
diff --git a/tests/root/contents.txt b/tests/root/contents.txt
index e052e04b2..280953b46 100644
--- a/tests/root/contents.txt
+++ b/tests/root/contents.txt
@@ -26,6 +26,7 @@ Contents:
    extensions
    doctest
    extensions
+   versioning/index
 
    Python <http://python.org/>
 
diff --git a/tests/root/versioning/added.txt b/tests/root/versioning/added.txt
new file mode 100644
index 000000000..22a70739c
--- /dev/null
+++ b/tests/root/versioning/added.txt
@@ -0,0 +1,20 @@
+Versioning test text
+====================
+
+So the thing is I need some kind of text - not the lorem ipsum stuff, that
+doesn't work out that well - to test :mod:`sphinx.versioning`. I couldn't find
+a good text for that under public domain so I thought the easiest solution is
+to write one by myself. It's not really interesting, in fact it is *really*
+boring.
+
+Anyway I need more than one paragraph, at least three for the original
+document, I think, and another one for two different ones.
+
+So the previous paragraph was a bit short because I don't want to test this
+only on long paragraphs, I hope it was short enough to cover most stuff.
+Anyway I see this lacks ``some markup`` so I have to add a **little** bit.
+
+Woho another paragraph, if this test fails we really have a problem because
+this means the algorithm itself fails and not the diffing algorithm which is
+pretty much doomed anyway as it probably fails for some kind of language
+respecting certain nodes anyway but we can't work around that anyway.
diff --git a/tests/root/versioning/deleted.txt b/tests/root/versioning/deleted.txt
new file mode 100644
index 000000000..a1a9c4c91
--- /dev/null
+++ b/tests/root/versioning/deleted.txt
@@ -0,0 +1,12 @@
+Versioning test text
+====================
+
+So the thing is I need some kind of text - not the lorem ipsum stuff, that
+doesn't work out that well - to test :mod:`sphinx.versioning`. I couldn't find
+a good text for that under public domain so I thought the easiest solution is
+to write one by myself. It's not really interesting, in fact it is *really*
+boring.
+
+So the previous paragraph was a bit short because I don't want to test this
+only on long paragraphs, I hope it was short enough to cover most stuff.
+Anyway I see this lacks ``some markup`` so I have to add a **little** bit.
diff --git a/tests/root/versioning/deleted_end.txt b/tests/root/versioning/deleted_end.txt
new file mode 100644
index 000000000..f30e63007
--- /dev/null
+++ b/tests/root/versioning/deleted_end.txt
@@ -0,0 +1,11 @@
+Versioning test text
+====================
+
+So the thing is I need some kind of text - not the lorem ipsum stuff, that
+doesn't work out that well - to test :mod:`sphinx.versioning`. I couldn't find
+a good text for that under public domain so I thought the easiest solution is
+to write one by myself. It's not really interesting, in fact it is *really*
+boring.
+
+Anyway I need more than one paragraph, at least three for the original
+document, I think, and another one for two different ones.
diff --git a/tests/root/versioning/index.txt b/tests/root/versioning/index.txt
new file mode 100644
index 000000000..234e223f1
--- /dev/null
+++ b/tests/root/versioning/index.txt
@@ -0,0 +1,11 @@
+Versioning Stuff
+================
+
+.. toctree::
+
+    original
+    added
+    insert
+    deleted
+    deleted_end
+    modified
diff --git a/tests/root/versioning/insert.txt b/tests/root/versioning/insert.txt
new file mode 100644
index 000000000..1c157cc90
--- /dev/null
+++ b/tests/root/versioning/insert.txt
@@ -0,0 +1,18 @@
+Versioning test text
+====================
+
+So the thing is I need some kind of text - not the lorem ipsum stuff, that
+doesn't work out that well - to test :mod:`sphinx.versioning`. I couldn't find
+a good text for that under public domain so I thought the easiest solution is
+to write one by myself. It's not really interesting, in fact it is *really*
+boring.
+
+So this paragraph is just something I inserted in this document to test if our
+algorithm notices that this paragraph is not just a changed version.
+
+Anyway I need more than one paragraph, at least three for the original
+document, I think, and another one for two different ones.
+
+So the previous paragraph was a bit short because I don't want to test this
+only on long paragraphs, I hope it was short enough to cover most stuff.
+Anyway I see this lacks ``some markup`` so I have to add a **little** bit.
diff --git a/tests/root/versioning/modified.txt b/tests/root/versioning/modified.txt
new file mode 100644
index 000000000..49cdad935
--- /dev/null
+++ b/tests/root/versioning/modified.txt
@@ -0,0 +1,17 @@
+Versioning test text
+====================
+
+So the thing is I need some kind of text - not the lorem ipsum stuff, that
+doesn't work out that well - to test :mod:`sphinx.versioning`. I couldn't find
+a good text for that under public domain so I thought the easiest solution is
+to write one by myself. Inserting something silly as a modification, btw. have
+you seen the typo below?. It's not really interesting, in fact it is *really*
+boring.
+
+Anyway I need more than one paragraph, at least three for the original
+document, I think, and another one for two different ones. So this is a small
+modification by adding something to this paragraph.
+
+So the previous paragraph was a bit short because I don't want to test this
+only on long paragraphs, I hoep it was short enough to cover most stuff.
+Anyway I see this lacks ``some markup`` so I have to add a **little** bit.
diff --git a/tests/root/versioning/original.txt b/tests/root/versioning/original.txt
new file mode 100644
index 000000000..b3fe06094
--- /dev/null
+++ b/tests/root/versioning/original.txt
@@ -0,0 +1,15 @@
+Versioning test text
+====================
+
+So the thing is I need some kind of text - not the lorem ipsum stuff, that
+doesn't work out that well - to test :mod:`sphinx.versioning`. I couldn't find
+a good text for that under public domain so I thought the easiest solution is
+to write one by myself. It's not really interesting, in fact it is *really*
+boring.
+
+Anyway I need more than one paragraph, at least three for the original
+document, I think, and another one for two different ones.
+
+So the previous paragraph was a bit short because I don't want to test this
+only on long paragraphs, I hope it was short enough to cover most stuff.
+Anyway I see this lacks ``some markup`` so I have to add a **little** bit.
diff --git a/tests/test_versioning.py b/tests/test_versioning.py
new file mode 100644
index 000000000..77306580c
--- /dev/null
+++ b/tests/test_versioning.py
@@ -0,0 +1,87 @@
+# -*- coding: utf-8 -*-
+"""
+    test_versioning
+    ~~~~~~~~~~~~~~~
+
+    Test the versioning implementation.
+
+    :copyright: Copyright 2007-2010 by the Sphinx team, see AUTHORS.
+    :license: BSD, see LICENSE for details.
+"""
+from util import *
+
+from docutils.statemachine import ViewList
+
+from sphinx.versioning import make_diff, add_uids, merge_doctrees
+
+def setup_module():
+    global app, original, original_uids
+    app = TestApp()
+    app.builder.env.app = app
+    app.connect('doctree-resolved', on_doctree_resolved)
+    app.build()
+    original = doctrees['versioning/original']
+    original_uids = [n.uid for n in add_uids(original, is_paragraph)]
+
+def teardown_module():
+    app.cleanup()
+    (test_root / '_build').rmtree(True)
+
+doctrees = {}
+
+def on_doctree_resolved(app, doctree, docname):
+    doctrees[docname] = doctree
+
+def test_make_diff():
+    tests = [
+        (('aaa', 'aaa'), (True, False, False)),
+        (('aaa', 'aab'), (False, True, False)),
+        (('aaa', 'abb'), (False, True, False)),
+        (('aaa', 'aba'), (False, True, False)),
+        (('aaa', 'baa'), (False, True, False)),
+        (('aaa', 'bbb'), (False, False, True))
+    ]
+    for args, result in tests:
+        assert make_diff(*args) == result
+
+def is_paragraph(node):
+    return node.__class__.__name__ == 'paragraph'
+
+def test_add_uids():
+    assert len(original_uids) == 3
+
+def test_modified():
+    modified = doctrees['versioning/modified']
+    new_nodes = list(merge_doctrees(original, modified, is_paragraph))
+    uids = [n.uid for n in modified.traverse(is_paragraph)]
+    assert not new_nodes
+    assert original_uids == uids
+
+def test_added():
+    added = doctrees['versioning/added']
+    new_nodes = list(merge_doctrees(original, added, is_paragraph))
+    uids = [n.uid for n in added.traverse(is_paragraph)]
+    assert len(new_nodes) == 1
+    assert original_uids == uids[:-1]
+
+def test_deleted():
+    deleted = doctrees['versioning/deleted']
+    new_nodes = list(merge_doctrees(original, deleted, is_paragraph))
+    uids = [n.uid for n in deleted.traverse(is_paragraph)]
+    assert not new_nodes
+    assert original_uids[::2] == uids
+
+def test_deleted_end():
+    deleted_end = doctrees['versioning/deleted_end']
+    new_nodes = list(merge_doctrees(original, deleted_end, is_paragraph))
+    uids = [n.uid for n in deleted_end.traverse(is_paragraph)]
+    assert not new_nodes
+    assert original_uids[:-1] == uids
+
+def test_insert():
+    insert = doctrees['versioning/insert']
+    new_nodes = list(merge_doctrees(original, insert, is_paragraph))
+    uids = [n.uid for n in insert.traverse(is_paragraph)]
+    assert len(new_nodes) == 1
+    assert original_uids[0] == uids[0]
+    assert original_uids[1:] == uids[2:]