This book is designed to be a physician's guide for those interested in diving and hyperbaric environments. It is not a detailed document for the erudite researcher; rather, it is a source of information for the scuba-diving physician who is searching for answers put to him by his fellow nonmedical divers. Following the publication of The Underwater Handbook: A Guide to Physiology and Performance for the Engineer there were frequent requests for a companion volume for the physician. This book is designed to fill the void. Production of the book has been supported by the Office of Naval Research and by the Bureau of Medicine and Surgery, Research and Development Command, under Navy Contract No. NOOOOI4-78-C-0604. Our heartfelt thanks go to the many authors without whose contributions the book could not have been produced. These articles are signed by the responsible authors, and the names a e also listed alphabetically in these preliminary pages. Every chapter was officially reviewed by at least one expert in the field covered and these reviewers are also listed on these pages. Our thanks go to them for their valuable assistance. We are grateful to Marthe Beckett Kent for editing Chapter III. Our thanks also go to Mrs. Carolyn Paddon for typing and retyping the manuscripts, and to Mrs. Catherine Coppola, who so expertly handled the many fiscal affairs.