South San Diego is a district within the City of San Diego, and is in the larger South Bay region of southwestern San Diego County, California. South San Diego is a practical exclave of San Diego, having no land connection with the rest of the city. It is the only part of the city which borders Mexico. South San Diego includes four of the city's official community planning areas: Otay Mesa, Otay Mesa-Nestor, San Ysidro, and the Tijuana River Valley.

The South Bay, also known as South County, is a region in southwestern San Diego County, California consisting of the cities and unincorporated communities of Bonita, Chula Vista, East Otay Mesa, Imperial Beach, Lincoln Acres, National City, and South San Diego.