The San Francisco 49ers (often referred to as the Niners) are a professional American football team. The team plays its home games in San Francisco, California, while the club's headquarters and practice facility are located in Santa Clara. The 49ers are currently a member of the Western Division of the National Football Conference (NFC) in the National Football League (NFL).

The 49ers began play in 1946 as a charter member of the All-America Football Conference (AAFC) and joined the NFL in 1950 after the AAFC merged into the older league. The team was the first NFL franchise to win 5 Super Bowls and is still the only team to win 5 in the span of 14 years. San Francisco is currently second only to the Pittsburgh Steelers in Super Bowl wins (tied with the Dallas Cowboys for five each). Including the "pre-SuperBowl" era, their 5 overall titles place them in a 4-way tie for fifth behind the Green Bay Packers (12), the Chicago Bears (9), the New York Giants (7), and the Steelers (6).

The 49ers teams of the 1980s and early 1990s were a great dynasty given their five Super Bowl triumphs in that span, including four in the 1980s. The Niners won 10 or more games for 16 straight seasons. Particularly notable seasons are the 1984 and 1989 teams. Three-time Super Bowl MVP Joe Montana, perennial Pro Bowler Ronnie Lott, all-time highest career quarterback rating holder Steve Young, and career touchdown leader Jerry Rice played for the 49ers during this period. Additionally, some of the most memorable plays (including "The Catch") and games (such as Super Bowl XXIII) were played by this team.

The name "49ers" comes from the name given to the gold prospectors who arrived in Northern California around 1849 during the California Gold Rush.