Scuba diving is the term used to describe the use of a Self Contained Underwater Breathing Apparatus to stay underwater for periods of time greater than the average individual can breath-hold. The diver self-propels underwater using fins attached to his/her feet. Some divers also move around with the assistance of a DPV (Diver Propulsion Vehicle), commonly referred to as a "scooter", or by using surface-tethered devices called sleds, which are pulled by a boat.

Divers are not limited to the use of scuba equipment in their sojourns underwater. While the Aqua-lung, developed by Emile Gagnan with assistance from Jacques-Yves Cousteau, is an "open-circuit" unit, rebreathers (both semi-closed circuit and closed circuit) and Surface-supplied systems are used depending on the needs of the diver.

Although scuba diving is still evolving, general classifications have grown up to describe the pursuits a diver might follow. These classifications include, but are not limited to: recreational diving, public safety diving, technical diving (aka Techy Divers), military diving and commercial diving. Within recreational diving there are those who are considered professional divers, because they maintain a professional standard of training and skills. Some consider Technical Diving to be a subset of recreational diving, while others separate it out due to the extensively different training equipment and knowledge required to execute technical dives. Public safety diving and military diving might likewise be classified as commercial diving because the practitioners make a living from their pursuit of diving. However, public safety divers (police or rescue) and military divers have a different mission than the typical commercial diver.