Montroll J. - Animal Origami for the Enthusiast.

This book begins with simple models and works up to more intricate ones. Each is folded from an uncut square. The book also contains a brief explanation of the symbols used to indicate various folds, and several pages explaining folds and "bases" considered basic. (Many models share the same initial folds; the result of some common beginning folds is called a base, e.g. "bird base", "frog base".)