This new version has been extended and updated, with new material added and new chapters. It takes all rudiments of decompression theory and phase mechanics to considerable depth, while focusing on diving applications in a historical perspective. Topics span many disciplines, and the targeted audience is the commercial diver, hyperbaric scientist, doctor, physical scientist, technical diver, and instructor. The intent of the 3rd Edition is to present a working view of decompression in diving, mostly focusing on theory with application, including equations. The discussion is neither a medical nor physiological synthesis. Such aspects are simplified, and for some certainly oversimplified. Nonetheless, it is directed toward the diver and reader with some rudimentary understanding of decompression. Background in the physical or life sciences is helpful but certainly not necessary. Discussed are the mechanics of tissue gas exchange, bubbles and nucleation, supersaturation, perfusion and diffusion. Also included are chapters on "Mixed Gases and Decompression" - "Decompression Tables, Meters and Models" - "Decompression Risks and Statistics." References and numerical examples (with solutions) are included for more detail and extended diver analysis.