Competitive swimwear refers to the swimsuit, clothing, equipment, and accessories used in the aquatic sports of swimming, diving, artistic swimming, triathlon, and water polo.

Some swimsuits are designed specifically for swimming competitions where they may be constructed of a special low resistance fabric that reduces skin drag. Most competitive swimmers wear special swimsuits including partial bodysuits, racerback styles, jammers and racing briefs to assist their glide through the water thus gaining a speed advantage.

For diving in water temperatures above 25 °C (77 °F), special bodysuits called "dive skins" are worn. These suits are made from spandex and provide little thermal protection, but they protect the skin from jellyfish stings, sunburn, and abrasion. This kind of suit is also known as a 'Stinger Suit'. Some divers wear a dive skin under a wetsuit, which allows easier donning and (for those who experience skin problems from neoprene) provides additional comfort.

Unlike regular swimsuits, which are designed mainly for aesthetic appearances, swimsuits intended to be worn during competitions are manufactured to assist the athlete in swimming competitions. They reduce friction and drag in the water, increasing the swimmer's forward motion efficiency. The tight fits allow for easy movement and are said to reduce muscle vibration, thus reducing drag. This also reduces the possibility that a high-forward dive will remove a diver's swimwear. Starting around 2000, to improve the effectiveness of the swimsuits, engineers have taken to designing them to replicate the skin of sea-based animals, sharks in particular.

In July 2009, FINA voted to ban non-textile (non-woven) swimsuits in competitive events from 2010. The new policy was implemented to combat the issues associated with performance-enhancing swimsuits, hindering the ability to accurately measure the performance of swimmers. Subsequently, the new ruling states that male swimsuits may maximally cover the area from the navel to the knee and female counterparts from the shoulder to the knee.

Some swimmers use a specialized training suit called drag suits to artificially increase drag during practice. Drag suits are swimwear with an outer layer of looser fabric – often mesh or nylon – to increase resistance against the water and build up the swimmer's endurance. They come in a variety of styles, but most resemble a looser fitting square-cut or swim brief.

The history of competitive swimwear has been dominated by concerns over public nudity in the first half of the 20th century and by efforts to reduce water drag in the second half. Those efforts initially lead male swimmers to reduce the early sagging one-piece swimsuits down to briefs only. Goggles were used in the crossing of the English Channel back in 1911, but only in 1970 appeared at international competitions. With the advent of rubber technology, latex swimming caps became mass-produced in the 1920s, and more efficient silicone caps appeared in the 1970s.

With the development of new materials that tightly fit the body and offered lower resistance to water than human skin, this trend was reversed to a complete body coverage from heels to neck and wrists. In 1999, Australian competitive swimmer Ian Thorpe signed with Adidas for an undisclosed six-figure sum, to race in their new bodysuit, although the national team was sponsored and wore outfits designed by Speedo. Thorpe's success in the 2000 Summer Olympics wearing the Adidas full-length black polyurethane bodysuit, in contrast to other swimmers wearing textile swimwear (males wore legskins, jammers, or briefs, while females wore racerback maillots), led to other swimming manufacturers such as Speedo and Mizuno to create their own rival bodysuits. Thorpe subsequently worked with Adidas which in 2003 released the Adidas Jetconcept bodysuit, whose design "came from the V-shaped grooves currently used on the wings and fuselage of civil aircraft".