Structural colors in living beings are one of the most marvelous arts that nature has ever created during the long history of the evolution. These colors originate from surprisingly sophisticated microstructures which gave rise to a new field of research?bionanophotonics. This book occupies a special position among similar books in the field of photonics, because it places a special emphasis on the detailed physical basis for the optical processes that are deeply connected with the structural colors, and also on the biological and physiological bases concerning what a variety of animals are living and how they are seen by human vision. In addition, it contains ample examples for the recent technological advances in photonics that are rooted in the nature.