Hyperbaric medicine involves using monoplace or multiplace hyperbaric chambers to deliver systemic oxygen under pressure to treat a number of medical conditions. The Undersea and Hyperbaric Medical Society approves the use of hyperbaric oxygen (HBO) for the following medical conditions: acute decompression illness, gas embolism, carbon monoxide poisioning, cyanide poisioning, clostridial gas gangrene and necrotizing soft tissue infections, compromised skin grafts and skin flaps, crush injury compartment syndrome and other acute traumatic ischemias, radiation tissue damage, refractory osteomyelitis, and selected problem wounds, acute exceptional blood loss anemia, acute thermal burns, and intracranial abscess. HBO use in treating these conditions is supported by controlled medical trials published in major peer‐reviewed journals and, as such, is evidence‐based. Numerous other experimental uses exist for HBO, such as for cardiac ischemia and for stroke, but these other uses have not yet been sufficiently proven to be beneficial. The effect of HBO is a result of the manifold increase in solubolized oxygen under pressure and its complex physiologic effects and, as such, is completely different from administering 100% oxygen at 1 Atmosphere. These affects include improving immune cell functioning and angiogenesis. More specific details of the history, physics, physiology, and function of HBO will be discussed as well as details of hyperbaric chamber facility design and safety.