This article reviews the applications of hyperbaric oxygen (HBO) as an adjunctive treatment of certain infectious processes. Infections for which HBO has been studied and is recommended by the Undersea and Hyperbaric Medicine Society include necrotizing fasciitis, gas gangrene, chronic refractory osteomyelitis (including malignant otitis externa), mucormycosis, intracranial abscesses, and diabetic foot ulcers that have concomitant infections. In all of these processes, HBO is used adjunctively along with antimicrobial agents and aggressive surgical debridement. This article describes the details of each infection and the research that supports the use of HBO.