Although strictly speaking the scuba set is only the diving equipment which is required for providing breathing gas to the diver, general usage includes the harness by which it is carried, and those accessories which are integral parts of the harness and breathing apparatus assembly, such as a jacket or wing style buoyancy compensator and instruments mounted in a combined housing with the pressure gauge.

Rebreather diving is used by recreational, military and scientific divers in applications where it has advantages over open circuit scuba, and surface supply of breathing gas is impracticable.

In commercial and military surface-supplied diving, a backup source of breathing gas is generally required, by regulatory legislation of code of practice, to be present in case the primary supply fails.

Surface-supplied diving equipment usually includes communication capability with the surface, which improves the safety and efficiency of the working diver.

[6] Surface-supplied air is provided on an open-circuit system, as it is simpler and more economical than recycling, and when supplied from the ambient atmosphere by a low pressure compressor, is practically unlimited.

[8] A diver's bailout set has a similar function, and is used to escape from an underwater situation where the primary breathing apparatus has failed for any reason.