The Complete Guide to Trapping (ISBN 1568300980)

It doesn't get better than this.:
Trapping is probably the least-understood portion of desktop publishing today. Lawler's book goes through just about every single bit of information you need - with easy-to-understand illustrations. Whether you're trapping in your application, or by using your RIP, this is an invaluable guide that will help put your knowledge right up there with the best pressmen.