The US Open, formally the United States Open Tennis Championships, is a major hard-court tennis tournament that has been played since 1881. The US Open is one of the most popular and prestigious tennis championships in the world and has been held annually in August and September over a two-week period. The US Open is one of the final tennis majors after the Australian Open, French Open, and Wimbledon, all of which comprise the Grand Slam each year. The main tournament consists of five different event championships: men's and women's singles, men's and women's doubles, mixed doubles, as well as additional tournaments for senior, junior, and wheelchair players. Since it's inception, The US Open has grown from an exclusive sporting event to a major championship in which more than 600 professional players compete for total prize money of over $21 million, with $1.5 million for each winner of the singles tournaments. 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.