The Oakland Athletics (often referred to as the A's) are an American professional baseball team based in Oakland, California. The Athletics compete in Major League Baseball (MLB) as a member club of the American League (AL) West division. The team plays its home games at the Oakland Coliseum. Throughout their history, the Athletics have won nine World Series championships.

One of the American League's eight charter franchises, the team was founded in Philadelphia in 1901 as the Philadelphia Athletics. They won three World Series championships in 1910, 1911, and 1913, and back-to-back titles in 1929 and 1930. The team's owner and manager for its first 50 years was Connie Mack and Hall of Fame players included Chief Bender, Frank "Home Run" Baker, Jimmie Foxx, and Lefty Grove. The team left Philadelphia for Kansas City in 1955 and became the Kansas City Athletics before moving to Oakland in 1968. Nicknamed the "Swingin' A's", they won three consecutive World Series in 1972, 1973, and 1974, led by players including Vida Blue, Catfish Hunter, Reggie Jackson, Rollie Fingers, and owner Charlie O. Finley. After being sold by Finley to Walter A. Haas Jr., the team won three consecutive pennants and the 1989 World Series behind the "Bash Brothers", Jose Canseco and Mark McGwire, as well as Hall of Famers Dennis Eckersley, Rickey Henderson and manager Tony La Russa.

Following the relocation of the Golden State Warriors across the Bay to San Francisco in 2019, and the relocation of the Raiders to Las Vegas in 2020, the Athletics became the only franchise in the five major American professional sports leagues located in the San Francisco Bay Area to play in Oakland.

From 1901 to 2021, the Athletics' overall win–loss record is 9,150–9,552 (.489).