California (/ˌkælɪˈfɔːrniə/) is a state in the Western United States that lies on the Pacific Coast. It borders Oregon to the north, Nevada and Arizona to the east, and shares an international border with the Mexican state of Baja California to the south. With almost 40 million residents across an area of 163,696 square miles (423,970 km²), it is the largest state by population, third-largest state by area and the largest state economy.

Prior to European colonization, California was one of the most culturally and linguistically diverse areas in pre-Columbian North America. European exploration in the 16th and 17th centuries led to the colonization by the Spanish Empire. The area became a part of Mexico in 1821, as a result of its successful war for independence. Following the U.S. conquest of California, part of the Mexican-American War, California was ceded to the United States in 1848. The California gold rush started in 1848 and led to social and demographic changes, including the California genocide. It organized itself and was admitted as the 31st state in 1850 as a free state, following the Compromise of 1850.

The Greater Los Angeles and San Francisco Bay Area areas are the nation's second- and fifth-most populous urban regions, with 19 million and 10 million residents respectively. Los Angeles is the state's most populous city and the nation's second-most. California's capital is Sacramento. Part of the Californias region of North America, the state's diverse geography ranges from the Pacific Coast and metropolitan areas in the west to the Sierra Nevada mountains in the east, and from the redwood and Douglas fir forests in the northwest to the Mojave Desert in the southeast. Two-thirds of the nation's earthquake risk lies in California. The Central Valley, a fertile agricultural area, dominates the state's center. The large size of the state results in climates that vary from moist temperate rainforest in the north to arid desert in the interior, as well as snowy alpine in the mountains. Droughts and wildfires are an ongoing issue, while simultaneously, atmospheric rivers are turning increasingly prevalent and leading to intense flooding events—especially in the winter.

The economy of California is the largest of any U.S. state, with an estimated 2024 gross state product of $4.172 trillion as of Q4 2024. It is the world's largest sub-national economy and, if it were an independent country, would be the fourth-largest economy in the world (putting it, as of 2025, behind Germany and ahead of Japan) when ranked by nominal GDP. The state's agricultural industry leads the nation in output, fueled by its production of dairy, almonds, and grapes. With the busiest port in the country (Los Angeles), California plays a pivotal role in the global supply chain, hauling in about 40% of goods imported to the US. Notable contributions to popular culture, ranging from entertainment, sports, music, and fashion, have their origins in California. Hollywood in Los Angeles is the center of the U.S. film industry and one of the oldest and largest film industries in the world; profoundly influencing global entertainment since the 1920s. The San Francisco Bay's Silicon Valley is the center of the global technology industry.

The Spaniards gave the name Las Californias to the peninsula of Baja California (in modern-day Mexico). As Spanish explorers and settlers moved north and inland, the region known as California, or Las Californias, grew. Eventually it included lands north of the peninsula, Alta California, part of which became the present-day U.S. state of California.

A 2017 state legislative document states, "Numerous theories exist as to the origin and meaning of the word 'California,'" and that all anyone knows is the name was added to a map by 1541 "presumably by a Spanish navigator."

The name is most likely derived from the mythical island of California in the fictional story of Queen Calafia, as recorded in a 1510 work The Adventures of Esplandián by Garci Rodríguez de Montalvo. Queen Calafia's kingdom was said to be a remote land rich in gold and pearls, inhabited by beautiful dark-skinned women who wore gold armor and lived like Amazons, and bred griffins for war.

Abbreviations of the state's name include CA, Cal., Cali, Calif., Califas, and US-CA.