In a calendar year, there are four Grand Slam tournaments in tennis. These tournaments are considered the most prestigious events in the sport. The Grand Slam tournaments are as follows:
1. Australian Open: Held annually in Melbourne, Australia, in January.
2. French Open (Roland Garros): Held annually in Paris, France, usually in May and June.
3. Wimbledon: Held annually in London, United Kingdom, typically in June and July.
4. US Open: Held annually in New York City, United States, usually in August and September.
These four tournaments collectively make up the Grand Slam circuit in tennis.