A swimsuit competition, more commonly now called a bikini contest, is a beauty contest which is judged and ranked while contestants wear a swimsuit, typically a bikini. One of the judging criteria is the physical attractiveness of the contestants. The Big Four international beauty pageants have included examples of such a competition.

Bikini contests have sometimes been organized or sponsored by companies for marketing purposes or to find new models for their products, with the contests being presented as a form of adult entertainment. Swimwear competitions have formed a part of beauty pageants, such as the Miss Earth and Miss World pageants, and sponsors have included commercial brands such as Hawaiian Tropic. Contests have also been held in bars and nightclubs, during intermissions in boxing or wrestling matches and at car shows. Bodybuilding and fitness competitions have evolved to include a bikini division. Participants in such contests may be competing for prizes including trophies, money, and modeling contracts.

In the United States, beauty pageants featuring women in bathing costumes became popular during the 1880s. However, such events were not regarded as respectable. The first "Miss America" pageant, held in 1921, made such contests somewhat more acceptable, although other, less well-tolerated beauty contests continued to be held as well. Miss America discontinued its swimsuit competition in 2018 to eliminate the criterion of contestants' physical appearance as a basis of judgment.

Bikini contests have sometimes been organised or sponsored by companies for marketing purposes or to find new models for their products. Miss Hawaiian Tropic is organized by Playtex to promote "Hawaiian Tropic", its suntan lotion. NOPI runs the annual Hot Import Nights bikini contest, which is held in conjunction with the import car-show in Atlanta, Georgia.

There is also an annual Hooters bikini competition.

Some swimsuit competitions, such as the Miss Bumbum contest, held in Brazil, and the Miss Reef contest, held in several South American countries, focus on the beauty of a single part of body, such as female buttocks.

Despite their popularity and women's voluntary participation, swimsuit competitions, especially bikini contests, are sometimes controversial. Critics argue that beauty contests reinforce the idea that girls and women are primarily valued for their physical appearance and pressure them to conform to conventional beauty standards.

The first Miss World contest was organized by Eric Morley in 1951 as a promotion for swimwear at the Festival of Britain. The press welcomed the spectacle and referred to it as Miss World. When the winner Kiki Håkansson from Sweden was crowned in a bikini, countries with religious traditions threatened to withdraw delegates. The bikinis were outlawed, and evening gowns were introduced instead. Håkansson remains the only Miss World to have been crowned in a bikini, an incident that was condemned by Pope Pius XII. The bikini was banned from Miss World beauty pageants after the controversy.