Free diving refers to dives made from surface to surface during voluntary apnoea on a single breath. No underwater breathing apparatus is used. Free diving (also often referred to as ‘breath-hold diving’ or ‘snorkel diving’) is regarded as the purest and most natural form of diving. Unencumbered by bulky equipment, the diver is free to move weightlessly and silently in the underwater world. Practised in some societies for thousands of years, free diving in its simplest form requires no equipment at all. The introduction of various performance-enhancing apparatus such as face masks, fins, weight belts, buoyancy vests and thermal protection suits may present new problems. For example, the addition of goggles or face masks allows for clear vision but introduces a gas space that must be ‘equalized’ to prevent barotrauma. Near the surface, wetsuits generate positive buoyancy that decreases as they are compressed during descent. If a weight belt is used to offset the initial positive buoyancy of the wetsuit, this will render the diver negatively buoyant as he or she begins the ascent. Nevertheless, recreational free divers and spearfishers often wear a mask, snorkel, fins, wetsuit and weights and carry a spear gun, knife and bag. Competitive free divers may also employ specialized devices such as weighted sleds for descent and inflatable lift bags for ascent to achieve remarkable depths. Even with such modern specialized equipment, human diving capabilities are paltry in comparison with those of marine mammals and other sea animals.