We've been viewing CVS as a kind of intelligent, coordinating library. However, it can also be thought of as a time machine (thanks to Jim Blandy for the analogy). So far, we've only seen how you can examine the past with CVS, without affecting anything. Like all good time machines, CVS also allows you to go back in time to change the past. What do you get then? Science fiction fans know the answer to that question: an alternate universe, running parallel to ours, but diverging from ours at exactly the point where the past was changed. A CVS branch splits a project's development into separate, parallel histories. Changes made on one branch do not affect the other.