On Film Editing : 
An Introduction to the Art of Film Construction
by Edward Dmytryk
Focal Press - ISBN: 0240517385

The second volume in Dmytryk's four book series, On Film. This is the closest anyone has come to describing the mechanics of film editing in an almost scientific manner. A good place to start if you know nothing about cutting film, and full of interesting anecdotes from nearly fifty years in the industry.