Half Moon Bay is a coastal city in San Mateo County, California, United States. Its population was 11,324 as of the 2010 census. Immediately at the north of Half Moon Bay is the Pillar Point Harbor and the unincorporated community of Princeton-by-the-Sea. The urban area had a population of 20,713 at the same census.

Half Moon Bay is a bay of the Pacific Ocean on the coast of San Mateo County, California. The bay is approximately semi-circular, hence the name half moon, with sea access to the south. Coastal towns located there are Princeton-by-the-Sea, Miramar, El Granada, and the city of Half Moon Bay.