California () is a state on the West Coast of the United States, along the Pacific Ocean. It is bordered by Oregon to the north, Nevada to the east, Arizona to the southeast, and to the south the Mexican state of Baja California. California is the most populous U.S. state. Its four largest cities are Los Angeles, San Diego, San Jose, and San Francisco. It is known for its varied climate and geography as well as its diverse population.

The area known as Alta California was colonized by the Spanish Empire beginning in the late 18th century. It and the rest of Mexico became an independent republic in 1821. In 1846 California broke away from Mexico, and after the Mexican-American War, Mexico ceded California to the United States. California became the 31st state admitted to the United States on September 9, 1850.

California is the third-largest U.S. state by land area. Its geography ranges from the Pacific coast to the Sierra Nevada mountains in the east, to Mojave desert areas in the southeast and the Redwood-Douglas fir forests of the northwest. The center of the state is dominated by the Central Valley, one of the most productive agricultural areas in the world.

The California Gold Rush (1848?1855) dramatically changed California with a large influx of people and an economic boom. The early 20th century was marked by Los Angeles becoming the center of the entertainment industry, in addition to the growth of a large tourism sector in the state. Along with California's prosperous agricultural industry, other industries include aerospace, petroleum, and computer and information technology. California ranks amongst the ten largest economies in the world, and were it a separate country, it would be 35th among the most populous countries.