More profound understanding of the nature of light and light-matter interactions in biology has enabled many applications in the biology and medical fields. So a new discipline is born, namely biophotonics. The aim of this book is to review the current state-of-the-art of the field by means of authoritative chapters written by the world leaders of the respective fields. Biosensors, biochips, optical tomography, optical microsurgery, photodynamics therapy, bioactivation of gene, photobiology of skin, and nanobiophotonics are each introduced and recent advances presented. This book will be useful not only to physicians, biologists, physicists, chemists, materials scientists, and engineers but also to graduate students who are interested in these rapidly developing fields.