diff --git a/vdirsyncer/sync.py b/vdirsyncer/sync.py
new file mode 100644
index 0000000..50be43c
--- /dev/null
+++ b/vdirsyncer/sync.py
@@ -0,0 +1,36 @@
+def sync(storage_a, storage_b, status):
+    '''Syncronizes two storages.
+
+    :param storage_a: The first storage
+    :param storage_b: The second storage
+    :param status: {uid: (etag_a, etag_b)}
+    '''
+    items_a = dict(storage_a.list_items())
+    items_b = dict(storage_b.list_items())
+    downloads_a = set()  # uids which to copy from a to b
+    downloads_b = set()  # uids which to copy from b to a
+    deletes_a = set()
+    deletes_b = set()
+
+    for uid in set(items_a) + set(items_b):
+        if uid not in status:
+            if uid in items_a and uid in items_b:  # missing status
+                status[uid] = (items_a[uid], items_b[uid])  # TODO: might need etag diffing too?
+            elif uid in items_a and uid not in items_b:  # new item in a
+                downloads_a.add(uid)
+            elif uid not in items_a and uid in items_b:  # new item in b
+                downloads_b.add(uid)
+        else:
+            if uid in items_a and uid in items_b:
+                if items_a[uid] != status[uid][0] and items_a[uid] != status[uid][1]:
+                    1/0  # conflict resolution
+                elif items_a[uid] != status[uid][0]:  # item update in a
+                    downloads_a.add(uid)
+                elif items_b[uid] != status[uid][1]:  # item update in b
+                    downloads_b.add(uid)
+                else:  # completely in sync!
+                    pass
+            elif uid in items_a and uid not in items_b:  # deleted from b
+                deletes_a.add(uid)
+            elif uid not in items_a and uid in items_b:  # deleted from a
+                deletes_b.add(uid)