The US Open, formally the United States Open Tennis Championships, is a hardcourt tennis tournament which is the modern iteration of one of the oldest tennis championships in the world, the U.S. National Championship, which for men's singles was first contested in 1881. Since 1987, the US Open has been chronologically the fourth and final tennis major comprising the Grand Slam each year; the other three are the Australian Open, French Open and Wimbledon. It is held annually in August and September over a two-week period (the weeks before and after Labor Day weekend). The main tournament consists of five different event championships: men's and women's singles, men's and women's doubles, and mixed doubles, with additional tournaments for senior, junior, and wheelchair players. Since 1978, the tournament has been played on acrylic hard courts at the USTA Billie Jean King National Tennis Center at Flushing Meadows-Corona Park in Queens, New York City.
The US Open has tiebreaks in every set, including the last set. The other three Grand Slam tournaments have tiebreaks in every set other than the last set (i.e. the fifth set for men and third set for women), and therefore their last set continues indefinitely until a two-game lead is reached.
The four Major tennis tournaments, also called the Slams, are the most important tennis events of the year in terms of world tour ranking points, tradition, prize-money awarded, strength and size of player field, and public attention. They are the Australian Open, the French Open, Wimbledon, and the US Open. Currently, both the Australian Open and the US Open are played on hard courts, while the French Open is played on clay, and Wimbledon is played on grass. The "Grand Slam" is the winning of all four Major tournaments in a single calendar year; however, it has also been used for many years now to refer to any of the major tournaments, (e.g., American tennis player Pete Sampras, who won 14 Major titles in his career, is often said to have won 14 "Grand Slams"—even though he did not achieve a true Grand Slam by winning all four Majors in a single year).
The Open Era of tennis began in 1968 when the Major tournaments agreed to allow professional players to compete. Wimbledon, the oldest of the Majors, was founded in 1877, followed by the US Open in 1881, the French Open in 1891, and the Australian Open in 1905. Beginning in 1905 and continuing to the present day, all four majors have been played yearly, with the exception of the two World Wars and 1986 for the Australian Open. The Australian Open is the 1st Major of the year (January), followed by the French Open (May–June), Wimbledon (June–July), and US Open (August–September).