Generally, the methods by which humans (or animals) move themselves through water without the aid of implements.
While it is possible that some groups of humans knew how to swim in prehistoric times (though there is no archaeological evidence for this), the first record of humans swimming occurred in approximately 2500 BC in places such as Egypt, Greece, Assyria, and Rome, and indeed citizens of Rome were taught to swim as boys. Australian Aborigines developed the fastest stroke, known as the Australian Crawl at some time (and may well have been using it well before the earliest recorded dates), which quickly spread and is the fastest swimming stroke.
Swimming remains a popular recreational activity, particularly in hot countries and in areas with natural watercourses, and a basic safety skill for those participating in on-water activities.
Competitive swimming became popular in the 19th century, and competitive swimming is a feature event at the Summer Olympic Games. There are four swimming disciplines, and there are events for different distances in those disciplines. Events are usually held in a pool of fifty metres in length, but recently "short-course" swimming events held in a 25 metre pool have become popular (if not held at the Olympics).
- Freestyle events place no restrictions on what action the competitors use. In practice, all freestyle events are swum using the Australian Crawl. Events are held at distances from 50 metres to 1500 metres.
- Butterfly events require that the swimmer's actions retain bilateral symmetry (the left side of the body has to do the same as the right). It is swum over 50, 100 and 200 metres. Butterfly, as it is typically performed, is the most strenuous stroke to maintain and few recreational swimmers can perform the stroke at all.
- Breaststroke places the additional restriction that the swimmer's arms must remain below the water at all times. It is the slowest stroke, and swum over 50, 100 and 200 metres.
- Backstroke places no symmetry restrictions, but swimmers must lay on their back at all times (except when turning) to perform the stroke. It is also swum over 50, 100 and 200 metres.
Additionally, there are "medley" events where swimmers successively perform the backstroke, breaststroke, butterfly, and then freestyle.
Competitive swimming has traditionally been dominated by the United States, but recently that dominance has been challenged by Australia, where swimming is a hugely popular recreational activity, and participant and spectator sport.
There are also competitions involving open-water swimming, and notable feats of open-water swimming endurance. Swimming across the English Channel is a popular challenge for these determined individuals.
Swimming is also an important part of the sport of Surf Lifesaving, which evolved from the training activities of rescuers who patrol popular swimming beaches and save those who tire or injure themselves out to sea.