Swimming is the self-propulsion of a person through water, or other liquid, usually for recreation, sport, exercise, or survival. Locomotion is achieved through coordinated movement of the limbs and the body to achieve hydrodynamic thrust that results in directional motion. Humans can hold their breath underwater and undertake rudimentary locomotive swimming within weeks of birth, as a survival response. Swimming requires stamina, skills, and proper technique.

Swimming is a popular activity and competitive sport where certain techniques are deployed to move through water. It offers numerous health benefits, such as strengthened cardiovascular health, muscle strength, and increased flexibility. It is suitable for people of all ages and fitness levels.

Swimming is consistently among the top public recreational activities, and in some countries, swimming lessons are a compulsory part of the educational curriculum. As a formalized sport, swimming is featured in various local, national, and international competitions, including every modern Summer Olympics.

Swimming involves repeated motions known as strokes to propel the body forward. While the front crawl, also known as freestyle, is widely regarded as the fastest of the four main strokes, other strokes are practiced for special purposes, such as training.

Swimming comes with certain risks, mainly because of the aquatic environment where it takes place. By way of example, swimmers may find themselves incapacitated by panic and exhaustion, both potential causes of death by drowning. Other dangers may arise from exposure to infection or hostile aquatic fauna. To minimize such eventualities, most facilities employ a lifeguard to keep alert for any signs of distress.

Swimmers often wear specialized swimwear, although depending on the area's culture, some swimmers may also swim nude or wear their day attire. In addition, a variety of equipment can be used to enhance the swimming experience or performance, including but not limited to the use of swimming goggles, floatation devices, swim fins, and snorkels.