Tennis is a racquet sport played between either two players ("singles") or two teams of two players ("doubles"). Players use a stringed racquet to strike a hollow rubber ball covered in felt over a net into the opponent's court.

Originating in England in the late 19th Century, the game spread first throughout the English-speaking world, particularly among the upper classes.

Tennis is now an Olympic sport that is played at all levels of society and by all ages in many countries around the world. Its rules have remained remarkably unchanged since the 1920s. Along with its millions of players, millions of people follow tennis as a spectator sport, especially the four Grand Slam tournaments.

Tennis is played on a rectangular flat surface, usually of grass, clay, or concrete (hard court). The court is 78 feet (23.77 m) long, and its width is 27 feet (8.23 m) for singles matches and 36 feet (10.97 m) for doubles matches. Additional clear space around the court is required in order for players to reach overrun balls. A net is stretched across the full width of the court, parallel with the baselines, dividing it into two equal ends. The net is 3 feet 6 inches (1.07 m) high at the posts, and 3 feet (914 mm) high in the center.

Tennis is usually a high intensity sport that requires at least a moderate fitness level.