Diving is an underwater activity that may either be performed as a hobby and recreational activity, or as a competitive sport. Sport diving is divided into two categories: freediving, where the divers hold their breath under water, or diving with an apparatus, which is more common. This is known as scuba diving. Scuba divers use a wetsuit or a drysuit, and equipment enabling them to breathe, which allows them to remain under water for a longer period of time.

There are many different types of underwater activities. Popular recreational activities under water include marine biology and marine archaeology, as well as underwater hunting (spearfishing). Competitive sports in the field of diving include team sports such as underwater rugby and underwater hockey, long-distance swimming with swim fins (finswimming), underwater photography and underwater hunting. Scuba diving requires a diving certificate. Anyone in good health can participate in diving, but normal lung function is essential, and a medical examination is usually required for the diving course.