Tennis is one of the most popular sports in the world, with numerous tournaments held throughout the year at various levels of competition. 

Here are some of the top tennis tournaments:

1. Grand Slam Tournaments: The four Grand Slam tournaments, also known as the Majors, are the most prestigious events in tennis. They are the Australian Open, French Open, Wimbledon, and the US Open. These tournaments are held annually and attract the best players from around the world.
2. ATP World Tour Finals: The ATP World Tour Finals, also known as the Nitto ATP Finals, is an annual men's tennis tournament featuring the top eight singles players and doubles teams in the world. The tournament is held at the end of the season and is considered the most prestigious event on the men's tour after the Grand Slams.
3. WTA Finals: The WTA Finals is the year-end tournament for the top-ranked women's singles and doubles players on the WTA tour. The tournament features the top eight players and doubles teams in the world and is held annually in different locations.
4. Masters 1000 Series: The Masters 1000 series is a group of nine men's tennis tournaments held annually around the world. These tournaments are the most prestigious after the Grand Slams and the ATP World Tour Finals.
5. Premier Mandatory and Premier 5 Tournaments: The Premier Mandatory and Premier 5 tournaments are the most prestigious events on the women's tour after the Grand Slams and the WTA Finals. There are five Premier Mandatory tournaments and four Premier 5 tournaments held annually.
6. Davis Cup: The Davis Cup is an annual men's international team tournament. It is considered the premier international team event in men's tennis, and countries compete against each other in a knockout format over the course of the year.
7. Fed Cup: The Fed Cup is the equivalent of the Davis Cup for women's tennis. It is an annual international team tournament in which countries compete against each other in a knockout format over the course of the year.

These are just some of the top tennis tournaments in the world. There are many other tournaments held throughout the year at various levels of competition, including Challenger and Futures events for up-and-coming players.