This book provides a comparative account of all the types of eye in the animal kingdom. It gives an outline of the structure and function of each kind of eye, with an emphasis on the nature of the optical systems and the physical principles involved in image formation. The book also covers the evolution and taxonomic distribution of each type of eye, and their roles in the behaviour and ecology of the animals that possess them. In comparing the capabilities of eyes, it considers the factors that lead to good resolution of detail, and to the ability to function under a wide range of light conditions. The book also deals with movements of the eyes: how they sample the world in time as well as space.