The physics, biology, engineering, physiology, medicine, and chemistry of diving center on pressure, and pressure changes. The average individual is subjected to atmospheric pressure swings of 3% at sea level, as much as 20% a mile in elevation, more at higher altitudes, and all usually over time spans of hours to days. Divers and their equipment can experience compressions and decompressions ... [Show full abstract] orders of magnitude greater, and within considerably shorter time scales. While the effects of pressure change are readily quantified in physics, chemistry, and engineering applications, the physiology, medicine, and biology of pressure changes in living systems are much more complicated. Increases in pressure with increasing depth impose many of the limitations in diving, applying equally well to the design of equipment. Early divers relied on their breathholding ability, while later divers used diving bells. Surface supplied air and SCUBA are rather recent innovations. With increasing exposure times and depths, divers encountered physiological and medical problems constraing activity, with decompression illness (DCI) perhaps the most noteworthy. By the 1880s, bubbles were noted in animals subjected to pressure reduction. By the 1900s, bubbles were postulated as the cause of DCI in divers and caisson workers. Within that postulate and drven by the need to optimize diver and aviator safety and time, decompression modeling has consolidated early rudimentary schedules into present more sophisticated tables and models. As basic knowledge and understanding of the biophysical effects of pressure change increase, so will the validity, reliability, and range of applicable models and algorithms used to stage diver ascents.