California is a U.S. state in the Western United States situated on the Pacific Coast. It borders Oregon to the north, Nevada and Arizona to the east, and shares an international border with Baja California to the south. As the largest U.S. state by population and third-largest by area, it encompasses diverse geography ranging from the Pacific Coast and metropolitan areas in the west to the Sierra Nevada mountains in the east.

Prior to European colonization, the region was one of the most culturally and linguistically diverse areas in pre-Columbian North America. Spanish exploration in the 16th and 17th centuries led to colonization, and the area became part of Mexico in 1821. Following the U.S. conquest during the Mexican-American War, California was ceded to the United States in 1848. It organized itself and was admitted as the 31st state in 1850 as a free state following the Compromise of 1850.

The state features distinct regions including Greater Los Angeles and the San Francisco Bay Area, which are among the nation's most populous combined statistical areas. Notable sites include Disneyland, the Golden Gate Bridge, Napa Valley wine country, and Mount Whitney, the tallest mountain in the contiguous United States. The Central Valley dominates the center as a fertile agricultural area, while the coast offers warm beaches and the interior contains arid deserts like Death Valley.

California's culture ranges from surf spots in Southern California to the glamor of Hollywood and the technology hubs of Silicon Valley. It has made substantial contributions to entertainment, technology, and innovation, including the American film industry, the personal computer, and the internet. Hollywood remains a vital center for the U.S. film industry, while the state is also known for its hippie counterculture, beach culture, and diverse agricultural output including dairy, almonds, and grapes.

The population was 39,538,223 as of 2020. The economy is the largest of any U.S. state, with an estimated 2025 gross state product of $4.296 trillion, making it the world's largest sub-national economy. The state experiences climates varying from moist temperate rainforest in the north to arid desert in the interior, alongside snowy alpine conditions in the mountains, with frequent wildfires and increasing weather whiplash.