Southern California (commonly shortened to SoCal) is a geographic and cultural region that generally comprises the southern portion of the U.S. state of California. Its densely populated coastal region includes Greater Los Angeles (the second-most populous urban agglomeration in the United States) and San Diego County (the second-most populous county in California). The region generally contains ten of California's 58 counties: Los Angeles, San Diego, Orange, Riverside, San Bernardino, Kern, Ventura, Santa Barbara, San Luis Obispo, and Imperial counties.

Although geographically smaller than Northern California in land area, Southern California has a higher population, with 23.76 million residents as of the 2020 census. The sparsely populated desert region of California occupies a significant portion of the area: the Colorado Desert, along with the Colorado River, is located on Southern California's eastern border with Arizona, and the Mojave Desert shares a border with Nevada to the northeast. Southern California's southern border with Baja California is part of the Mexico–United States border.

Southern California encompasses eight metropolitan areas (MSAs), three of which together form the Greater Los Angeles Combined Statistical Area (CSA) with over 18 million people, the second-biggest CSA after the New York CSA. These three MSAs are the Los Angeles metropolitan area (Los Angeles and Orange counties, with 13.3 million people), the Inland Empire (Riverside and San Bernardino counties, including the Coachella Valley cities, with 4.3 million people), and the Oxnard–Thousand Oaks–Ventura metropolitan area (0.8 million people). In addition, Southern California contains the San Diego metropolitan area with 3.3 million people, Bakersfield metro area with 0.9 million, and the Santa Barbara, San Luis Obispo, and El Centro (Imperial County) metropolitan areas.

The Southern California Megaregion (or megalopolis) is larger still, extending northeast into Las Vegas, Nevada and south across the Mexican border into Tijuana.

Within Southern California are two major cities, Los Angeles and San Diego, as well as three of the country's largest metropolitan areas. With a population of approximately 4 million, Los Angeles is the most populous city in California and the second most populous in the United States. South of Los Angeles and with a population of approximately 1.4 million is San Diego, the second most populous city in the state and the eighth most populous in the nation.

The counties of Los Angeles, San Diego, Orange, Riverside, and San Bernardino are the five most populous in the state, and are among the top 15 most populous counties in the United States.

The motion picture, television and music industry are centered in the Los Angeles area in Southern California. Hollywood, a district of Los Angeles, gives its name to the American motion picture industry, which is synonymous with the neighborhood name. Headquartered in Southern California are The Walt Disney Company (which owns ABC), Sony Pictures, Universal Pictures, MGM, Paramount Pictures, and Warner Bros. Universal, Warner Bros., and Sony also run major record companies.

Southern California is also home to a large surf and skateboard culture. Companies such as Vans, Volcom, Quiksilver, No Fear, Stüssy, and Body Glove are all headquartered there. Skateboarder Tony Hawk; surfers Rob Machado, Timmy Curran, Bobby Martinez, Pat O'Connell, Dane Reynolds, and Chris Ward live in Southern California. Some of the most famous surf locations are in Southern California as well, including Trestles, Rincon, The Wedge, Huntington Beach, and Malibu. Some of the world's largest action sports events, including the X Games, Boost Mobile Pro, and the U.S. Open of Surfing, are held in Southern California. The region is also important to the world of yachting with premier events including the annual Transpacific Yacht Race, or Transpac, from Los Angeles to Hawaii. San Diego Yacht Club hosted the three America's Cup races from 1988 to 1995. The first modern-era triathlon was held in San Diego's Mission Bay in 1974. Since then, Southern California, and San Diego in particular, have become a mecca for triathlon and multi-sport racing, products, and culture.