Swimming is a self-propelled way of people through fresh water or salt water, usually used for entertainment, sports, exercise or survival. Movement is achieved by coordinated movement of limbs, body or both. It's an evolutionary response that humans can hold their breath and perform basic locomotive swimming in the weeks after birth.

Swimming has always been one of the most important public recreational activities. In some countries, swimming is a compulsory part of education curriculum. As a formal sport, swimming takes part in various local, national and international competitions, including every modern Summer Olympic Games.

Swimming depends on the natural / unnatural buoyancy of the human body. On average, the relative density of the human body is 0.98 compared with that of water, which makes the human body float. However, buoyancy varies according to body composition and water salinity. Higher body fat and salt water reduce the relative density of the body and increase its buoyancy.

Because the density of human body is only a little less than water, water supports the weight of body when swimming. Therefore, compared with land activities such as running, swimming is "low impact". The density and viscosity of water also create resistance to objects passing through it. Swimming strokes use this resistance to generate propulsion, but the same resistance also creates resistance on the body.

Hydrodynamics is important for stroke techniques that swim faster, and swimmers who want to swim faster or reduce exhaust try to reduce their body's resistance to movement in the water. In order to improve hydrodynamic performance, swimmers can increase the strength of the stroke and reduce the water resistance, although the strength must be increased three times to achieve the same effect as reducing resistance. Effective swimming by reducing water resistance involves rolling the body at horizontal water levels to reduce the width of the body in the water and extending the arms as far as possible to reduce wave resistance.

Before jumping into the pool, swimmers may do exercises such as squatting. Squatting can increase the swimmer's starting speed by heating the thigh muscles.