Marine Corps Recruit Depot San Diego is a United States military installation in San Diego, California. It is adjacent to the closed Naval Training Center in the same city, as well as Lindbergh Field, which serves as an international airport for the city of San Diego, and Interstate 5.

The base is along the Pacific Ocean and concerns itself primarily with the training of new United States Marine recruits, specifically male recruits from west of the Mississippi River. All other recuits are trained at MCRD Parris Island in South Carolina.

During basic training, commonly referred to as boot camp, recruits complete drill, physical training, swim qualification and other training possible in a garrison environment aboard MCRD. At some point near the end of the training cycle, recruit companies move to Edson Range aboard Marine Corps Base Camp Pendleton where they spend four weeks training on the rifle range, qualifying with the rifle and engaging in field training, including a 54-hour evolution known as 'The Crucible'.

Aboard MCRD San Diego are also Drill Instructor and Recruiter schools, which train Drill Instructors and recruiters for the United States Marine Corps. Other facilities aboard MCRD contribute housing, medical and morale welfare and recreation (MWR) facilities for the large San Diego military community.

Marine Corps presence in San Diego dates back to July 1914, but ground was not broken for a permanent base until 2 March 1919, after Joseph Henry Pendleton (for whom Camp Pendleton was later named) successfully fought for a base in the area. By 1921, the base was formally commissioned and in 1923, it became the primary recruiting center for the west coast. During World War II, the base almost exclusively dealt with recruiting. In 1948, the base was formally named MCRD San Diego.