The western border of Santa Monica, California, is the 3-mile (4.8 km) stretch of Santa Monica Bay. On its other sides, the city is bordered by various districts of Los Angeles: the northwestern border is Pacific Palisades, the eastern border is Brentwood north of Wilshire Boulevard and West Los Angeles south of Wilshire, the northeastern border is generally San Vicente Boulevard up to the Riviera Country Club, the southwestern border is Venice Beach and the southern border is with West Los Angeles and Mar Vista.

Santa Monica Bay is a bight of the Pacific Ocean in Southern California, United States. Its boundaries are slightly ambiguous, but it is generally considered to be the part of the Pacific within an imaginary line drawn between Point Dume, in Malibu, and the Palos Verdes Peninsula. Its eastern shore forms the western boundary of the Los Angeles Westside and South Bay regions. Although it was fed by the Los Angeles River until the river's catastrophic change of course in 1825, the only stream of any size now flowing into it is Ballona Creek. Smaller waterways draining into the bay include Malibu Creek, Topanga Creek, and Santa Monica Creek.