A mode of diving, or diving mode, is a particular way to dive underwater that requires specific equipment, procedures and techniques, and may expose the diver to a particular range of hazards.
There are several modes of diving; these are distinguished by the type of breathing apparatus, diving equipment, procedures and techniques involved, and whether the diver is exposed to ambient pressure. Ambient pressure diving includes freediving and compressed-gas diving, which may also be classed as air diving, oxygen diving, and mixed gas diving by the breathing gas used, and as open-circuit, semi-closed, or closed-circuit depending on the type of breathing apparatus used. There is also atmospheric pressure diving, which involves encapsulation in an atmospheric pressure diving suit or submersible, and unmanned diving, where there are no human divers involved. The diving equipment, support equipment and procedures used largely depend on the mode of diving.