Snorkeling (British and Commonwealth English spelling: snorkelling) is the practice of swimming face down in a body of water while breathing the ambient air through a shaped tube called a snorkel, usually with swimming goggles or a diving mask, and swimfins. In cooler waters, a wetsuit is also worn. The use of this equipment allows the snorkeler (British and Commonwealth English spelling: snorkeller) to observe the underwater environment for extended periods with relatively little effort, and to breathe while face-down at the surface.

Snorkeling is a popular recreational activity, particularly at tropical resort locations. It provides the opportunity to observe underwater life^{[broken anchor]} in a natural setting without the complicated equipment and training required for scuba diving. It appeals to all ages because of how little effort is involved and is the basis of the two surface disciplines of the underwater sport of finswimming.

Snorkeling is also used by scuba divers when at the surface, in underwater sports such as underwater hockey and underwater rugby, and as part of water-based searches conducted by search and rescue teams.

Essential equipment includes the snorkel for breathing, and a diving mask or swimming goggles for vision. Swimfins for more efficient propulsion are common. Environmental protection against cold, sunburn, and marine stings and scratches is also regionally popular, and may be in the form of a wetsuit, dry suit, dive skins, or rash vest. Some snorkelers rely on waterproof sunscreen lotions, but some of these are environmentally damaging. If necessary, the snorkeler may wear a weightbelt to facilitate freediving, or an inflatable snorkeling vest, a form of buoyancy aid, for safety.

A snorkel is a device used for breathing air from above the surface when the wearer's head is facing downwards in the water with the mouth and the nose submerged. It may be either separate or integrated into a swimming or diving mask. The integrated version is only suitable for surface snorkeling, while the separate device may also be used for underwater activities such as spearfishing, freediving, finswimming, underwater hockey, underwater rugby and for surface breathing with scuba equipment. A swimmer's snorkel is a tube bent into a shape often resembling the letter "L" or "J", fitted with a mouthpiece at the lower end and constructed of light metal, rubber or plastic. The snorkel may come with a rubber loop or a plastic clip enabling the snorkel to be attached to the outside of the head strap of the diving mask. Although the snorkel may also be secured by tucking the tube between the mask strap and the head, this alternative strategy can lead to physical discomfort, mask leakage or even snorkel loss.

Snorkels constitute respiratory dead space. When the user takes in a fresh breath, some of the previously exhaled air which remains in the snorkel is inhaled again, reducing the amount of fresh air in the inhaled volume, and increasing the risk of a buildup of carbon dioxide in the blood, which can result in hypercapnia. The greater the volume of the tube, and the smaller the tidal volume of breathing, the more this problem is exacerbated. A smaller diameter tube reduces the dead volume, but also increases resistance to airflow and so increases the work of breathing. Including the internal volume of the mask in the breathing circuit greatly expands the dead space. Occasional exhalation through the nose while snorkeling with a separate snorkel will slightly reduce the buildup of carbon dioxide, and may help in keeping the mask clear of water, but in cold water, it will increase fogging. To some extent the effect of dead space can be counteracted by breathing more deeply and slowly, as this reduces the dead space ratio and work of breathing.

Snorkels come in two orientations: Front-mounted and side-mounted. The first snorkel to be patented in 1938 was front-mounted, worn with the tube over the front of the face, and secured with a bracket to the diving mask. Front-mounted snorkels proved popular in European snorkeling until the late 1950s when side-mounted snorkels came into the ascendancy. Front-mounted snorkels experienced a comeback a decade later as a piece of competitive swimming equipment to be used in pool workouts and in finswimming races, where they outperform side-mounted snorkels in streamlining.

A plain snorkel consists essentially of a tube with a mouthpiece to be inserted between the lips.