A square dance is a dance for four couples, or eight dancers in total, arranged in a square, with one couple on each side, facing the middle of the square. Square dances are part of a broad spectrum of dances known by various names: country dances, traditional dances, folk dances, barn dances, ceilidh dances, contra dances, Playford dances, etc. These dances appear in over 100 different formations, of which the Square and the Longways Set are by far the most popular formations.

Square dances contain elements from numerous traditional dances including English country dances, which were first documented in 17th-century England, and 18th-century French quadrilles and cotillions; square dancing travelled to North America with the European settlers and developed significantly there.

Square dancing is done in many different styles all around the world. In some countries and regions, through preservation and repetition, square dances have attained the status of a folk dance. Square dancing is strongly associated with the United States, in part due to its association with the romanticized image of the American cowboy in the 20th century, and 31 states have designated it as their official state dance. The main North American types of square dances include traditional square dance and modern western square dance, which is widely known and danced worldwide. Other main types popular in England, Ireland, and Scotland include Playford dances, regional folk dances, ceili, Irish set dances, and Scottish country dances.

The couples in a square are numbered, although numbering varies among different types. In many of the types, two of the couples are known as heads and the other two are called sides. In most American forms of square dance, the dancers are prompted or cued through a sequence of steps by a caller to the beat (and, in some traditions, the phrasing) of music. In other variations, dancers have no caller and instead memorize and perform a specific routine and sequence of steps. Square dance music varies widely, with some forms using traditional tunes and others employing more modern types.

Dances can be organized by square dance clubs, bands, individuals, or similar organizations. Attire varies by type, with some forms possessing a specific dress code and others having no requirements. The standard square formation can also vary at times to include more or fewer dancers or arrange dancers in a different shape.

The origins of Square dances can be traced back to steps and figures used in traditional folk dances and social dances from many countries. One of the earliest influences may have been the Morris dance, an English dance for six men involving a line formation and energetic steps. This dance is closely related to another ancestor of square dancing, English country dance, which included a variety of dances for groups of couples arranged in circles, lines, or squares. In 1651, John Playford published 105 of these dances in The English Dancing Master, eight of which are square dances exhibiting concepts still in use, such as the head couples performing an action and the side couples repeating it. Three of the dances, such as "Dull Sir John", specifically use the term square dance in the phrase, "A Square Dance for eight thus". In the early 1800s, English country dances merged with French dances to form the quadrille, a dance for four couples in a square.

These dances further evolved in America, where they arrived with European settlers. After the American Revolution, the quadrille became especially popular. Quadrilles were originally danced from memorized steps and sequences, but as African American slaves played music for the dances, they began calling out the steps. This practice became common by the early 1900s and gave rise to the modern caller. Between 1940 and 1960, modern western square dance evolved from the western style of traditional square dance that had formed in the United States. Traditional western square dancing was promoted beginning in the 1930s by Lloyd Shaw, who solicited definitions from callers across the country in order to preserve that dance form and make it available to other teachers. The American folk music revival in New York City in the 1950s was rooted in the resurgent interest in square dancing and folk dancing there in the 1940s, which gave musicians such as Pete Seeger popular exposure.

Starting in the 1970s, many U.S. states adopted square dance as their state dance, the result of a campaign by square dancers to make it the national dance.