California is a state in the Pacific Region of the United States. With 39.6 million residents across a total area of about 163,696 square miles (423,970 km²), California is the most populous U.S. state and the third-largest by area. The state capital is Sacramento. The Greater Los Angeles Area and the San Francisco Bay Area are the nation's second- and fifth-most populous urban regions, with 18.7 million and 9.7 million residents respectively. Los Angeles is California's most populous city, and the country's second-most populous, after New York City. California also has the nation's most populous county, Los Angeles County, and its largest county by area, San Bernardino County. The City and County of San Francisco is both the country's second-most densely populated major city after New York City and the fifth-most densely populated county, behind only four of the five New York City boroughs.

California's economy, with a gross state product of $3.0 trillion, is larger than that of any other U.S. state and is the largest sub-national economy in the world. If it were a country, California would be the fifth-largest economy in the world (larger than the United Kingdom, France, or India), and the 36th-most populous . The Greater Los Angeles Area and the San Francisco Bay Area are the nation's second- and third-largest urban economies ($1.253 trillion and $907 billion respectively ), after the New York metropolitan area. The San Francisco Bay Area PSA had the nation's highest gross domestic product per capita in 2017 (~$94,000) among large primary statistical areas, and is home to three of the world's ten largest companies by market capitalization and three of the world's ten richest people.

California culture is considered a global trendsetter in popular culture, communication, information, innovation, environmentalism, economics, politics, and entertainment. As a result of the state's diversity and migration, California integrates foods, languages, and traditions from other areas across the country and around the globe. It is considered the origin of the American film industry, the hippie counterculture, fast food, beach and car culture, the Internet, and the personal computer, among others. The San Francisco Bay Area and the Greater Los Angeles Area are widely seen as centers of the global technology and entertainment industries, respectively. California's economy is very diverse: 58% of it is based on finance, government, real estate services, technology, and professional, scientific, and technical business services. Although it accounts for only 1.5% of the state's economy, California's agriculture industry has the highest output of any U.S. state.

California shares a border with Oregon to the north, Nevada and Arizona to the east, and the Mexican state of Baja California to the south. The state's diverse geography ranges from the Pacific Coast in the west to the Sierra Nevada mountain range in the east, and from the redwood and Douglas fir forests in the northwest to the Mojave Desert in the southeast. The Central Valley, a major agricultural area, dominates the state's center. Although California is well-known for its warm Mediterranean climate, 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. Over time, drought and wildfires have become more frequent challenges.