Even in ancient times, breathing was believed to be the most important feature of life itself. The very Universe was viewed as a huge breathing organism, within which every part was related to everything else through a process of vibration - or breath. Nowadays, our understanding of the laws governing the Universe and life has advanced tremendously. Yet this has not changed our perception of breathing as one of the most important mechanisms of life support. Books on human respiration are usually written either only by physicians or engineers. This book became possible as a result of a decade of research collaboration between physicians, engineers, physicists and applied mathematicians. Consequently, this volume presents the latest developments and major challenges in the area of biomedical engineering concerned with studies of the human respiratory system. The contributors cover the anatomy and physiology of human respiration, some of the newest macro- and microscopic models of the respiratory system, numerical simulation and computer visualisation of gas transport phenomena, and applications of these models to medical diagnostics, treatment and safety.