Tennis is a game played between two players (singles) or between two teams of two players (doubles). Players use a stringed racquet to strike a hollow rubber ball covered with felt over a net into the opponent\'s court. Originating in Europe in the late 19th century, tennis spread first throughout the English-speaking world, particularly among the upper classes. Tennis is now once again an Olympic sport and is played at all levels of society, by all ages, and in many countries around the world. Except for the adoption of the tie-breaker in the 1970s, its rules have remained remarkably unchanged since the 1890s. Along with its millions of players, millions of people follow tennis as a spectator sport, especially the four Grand Slam tournaments: Australian Open, French Open, Wimbledon, and the U.S. Open.