This book is at the same time an index of known optical illusions, and an essay on the reasons they exist. Abundantly illustrated, the illusions in this collection are organized according to the type of effect they produce. This is both an art book and a science text. Ninio explains how illusions are produced by saturating our visual channels such that our brains are obliged to identify something recognizable. Because our senses are limited, we make judgements without having really understood what we have seen. Ninio examines why we make mistakes in distance and form recognition, showing how illusion can be a powerful instrument of neurological and physiological inquiry.Biologist Jacques Ninio is research director at CNRS.