The Cincinnati Open, also known as the Cincinnati Masters and as the Western & Southern Open for sponsorship reasons, is a men's and women's professional tennis tournament played in the United States.

The men's tournament belongs to the ATP Tour Masters 1000 category, which is the most important category after the Grand Slam tournaments and the ATP Finals, as well as the women's tournament which belongs to the WTA 1000 category.

The competition takes place on the hard courts of Lindner Family Tennis Center in Mason, a suburb of the city of Cincinnati (Ohio), in August. The tournament began in 1899 as the Cincinnati Open.

The term Open did not refer to opening to professionals, but to opening the tournament to non-Cincinnati residents. It was voted by tennis players as the best category tournament in 1986, and the Premier category in 2014.

Bill Talbert has the record for combined wins (singles and doubles in the same year) three, in 1943, 1945 and 1947 among men, while Clara Louise Zinke holds it among women with 4 wins (1927, 1928, 1930, 1931) . In 1931 Zinke won all events (singles, doubles and mixed doubles) as had May Sutton in 1906, and in men's Raymond Little in 1901.