Swimming is consistently found to be amongst the top recreational activities undertaken by the public, and in some countries, swimming lessons are a compulsory part of the educational curriculum. As a formalised sport, swimming features in a range of local, national and international competitions, including featuring in every modern summer Olympics.

Swimming is primarily a cardiovascular/aerobic exercise[8] due to the long exercise time, requiring a constant oxygen supply to the muscles, except for short sprints where the muscles work anaerobically. As with most aerobic exercise, swimming is believed to reduce the harmful effects of stress. Swimming can also improve posture.

Swimming can be undertaken using a wide range of different styles, known as "strokes", and these strokes are used for a different purposes, or to distinguish between classes in competitive swimming. It is not necessary to use a defined stroke for propulsion through the water, and untrained swimmers may use a "doggy paddle" of arm and leg movements which mimics the strokes of quadruped animals such as dogs in the water.