Snorkeling (British spelling: snorkeling) is the practice of swimming on or through a body of water while equipped with a diving mask, a shaped tube called a snorkel, and usually swim fins. In cooler waters, a wetsuit may also be worn. Using this equipment allows the snorkeler to observe underwater attractions for extended periods of time with relatively little effort.
It is a popular recreational activity, particularly at tropical resort and diving locations. Snorkeling is also employed by scuba divers when on the surface, and search teams may snorkel as part of a water-based search.

The primary attraction of snorkeling is the opportunity to observe underwater life in a natural setting without the complicated equipment and training required for scuba diving, and without the exhaled bubbles of scuba-diving equipment. Snorkeling is also a means to an end in popular sports such as underwater hockey, underwater ice hockey, underwater rugby and spear fishing.

Although donning a mask and snorkel and swimming in any body of water would technically constitute "snorkeling," by and large it is generally accepted that a "snorkeler" would don such gear and practice such activity within the vicinity of a reef, wreck, underwater formation or other submerged objects either to observe fish, plants, organisms and/or formations. Being non-competitive, snorkeling is less a sport and more a leisure activity.

Snorkeling requires no special training, only the ability to swim and to breathe through the snorkel. However, for safety reasons, instruction and orientation from a fellow "experienced" snorkeler, tour guide, dive shop, or equipment rental shop is recommended. Instruction generally covers equipment usage, basic safety, what to look for, and what to look out for, and conservation instructions (fragile organisms such as coral are easily damaged by divers and snorkelers). As with scuba-diving it is always recommended that one not snorkel alone, but rather with a "buddy", a guide or a tour group.

Some commercial snorkeling locations require snorkelers to wear an inflatable vest, similar to a personal flotation device. They are usually bright yellow or orange and have a device that allows users to inflate or deflate the device to adjust their buoyancy. However these devices hinder and prevent a snorkeler from free diving to any depth. A wetsuit of appropriate thickness and coverage is suggested as they do provide some buoyancy without as much resistance to submersion.

Experienced snorkelers often start to investigate amateur free-diving, which should be preceded by at least some training from a dive instructor or experienced free-diver.