The National Association of Underwater Instructors is a nonprofit association of scuba instructors. It primarily serves as a recreational dive certification and membership organization established to provide international diver standards and education programs. The agency was founded in 1960 by Albert Tillman and Neal Hess. NAUI is headquartered in the Tampa, Florida area with dive and member instructors, resorts, stores, service and training centers located around the world.

Scuba diving is a mode of underwater diving whereby divers use breathing equipment that is completely independent of a surface breathing gas supply, and therefore has a limited but variable endurance. The name scuba is an anacronym for "Self-Contained Underwater Breathing Apparatus" and was coined by Christian J. Lambertsen in a patent submitted in 1952. Scuba divers carry their own source of breathing gas, usually compressed air, affording them greater independence and movement than surface-supplied divers, and more time underwater than free divers. Although the use of compressed air is common, a gas blend with a higher oxygen content, known as enriched air or nitrox, has become popular due to the reduced nitrogen intake during long or repetitive dives. Also, breathing gas diluted with helium may be used to reduce the effects of nitrogen narcosis during deeper dives.