Flutter, Skitter, and Skim by Leonard M. Wright Jr.

This is the book that revolutionized the way fly fishing is done. Originally written in 1972, Fishing the Dry Fly as a Living Insect (now Flutter, Skitter and Skim: Using the Living Insect as a Guide to Successful Fly Fishing) changed the method of fly fishing from one of casting the fly upstream and allowing it to "dead drift" with the current to including tactics that recreate the movement of an abundant aquatic insect-the caddis. Wright explains the behavior of the caddis and the best tactics to take advantage of them.