Respiration is a unique topic among various subdisciplines of physiology. Physiolo­ gists and clinicians are now able to communicate quantitative functional properties of lung mechanics and gas exchange in the language of the engineer, physicist and mathematician. This is largely due to intensive and stimulating work during the last decades of brilliant minds in a handful of excellent schools in the international family of physiologists. Among these founders of respiratory physiology are a number of clinicians, and they have. taken significant , part both in shaping the theoretical knowledge to clinical applicability and developing technical devices for diagnosis and therapy in pulmonology. However, the theory behind the evaluation of measure­ ments, and their interpretation in terms of clinical function tests, is so confusingly complex that the ordinary physician, not specifically trained in respiratory physiol­ ogy, finds himself unable to critically apply these techniques. We, therefore, need descriptions of respiratory physiology and of its clinical application presented in the language of the clinician. And that is what this book is meant to be. Written by an expert in electrical and biomedical engineering, and by an expert in intensive care medicine, this text constitutes an "operational manual" of clinical respiratory physiology. It does not intend to be another textbook of basic respiratory physiology or pathophysiology. This book not only addresses practical clinicians, particularly those of intensive care medicine, by describing the essentials of clinically relevant respiratory knowledge.