This book is a biophysically grounded comparative survey of how animals detect light and image in their world. Included are discussions of photoreceptors, light emitters, and eyes. The book centres on the kinds of optical systems that have evolved, beginning with unicellular organisms that detect and respond to light. The book details how these systems developed into more advanced and complex designs for imaging. Wolken's book will appeal to biologists, bioengineers and researchers working in the area of visual optics.