Belmont is an affluent city in San Mateo County in the U.S. state of California. It is in the San Francisco Bay Area, on the San Francisco Peninsula halfway between San Francisco and San Jose. It was originally part of Rancho de las Pulgas, for which one of its main roads, the Alameda de las Pulgas, is named. The city was incorporated in 1926. Its population was 25,835 at the 2010 census.

Ralston Hall is a historic landmark built by Bank of California founder, William Chapman Ralston, on the campus of Notre Dame de Namur University. It was built around a villa formerly owned by Count Cipriani, an Italian aristocrat. The locally famous “Waterdog Lake” is also located in the foothills and highlands of Belmont.

One of two surviving structures from the Panama-Pacific International Exposition is on Belmont Avenue (the other is the Palace of Fine Arts in San Francisco). The building was brought to Belmont by E.D. Swift shortly after the exposition closed in 1915. Swift owned a large amount of land in the area.

Carlmont High School and Ralston Middle School are located in Belmont and are both Distinguished California Schools.

Belmont has attracted national attention for a smoking ordinance passed in January 2009 which bans smoking in all businesses and multi-story apartments and condominiums; the ordinance has been described as one of the strictest in the nation.