Baja California (ˈbɑːhɑː_kælɨˈfɔrnjə, ˈbaxa kaliˈfornjalang, lit. "Lower California"), officially Free and Sovereign State of Baja California (Estado Libre y Soberano de Baja California), is one of the 31 states which, with the Federal District, comprise the 32 Federal Entities of Mexico. It is both the northernmost and westernmost state of Mexico, but before becoming a state in 1953, the area was known as the North Territory of Baja California. It has an area of 70113 km², or 3.57% of the land mass of Mexico and comprises the northern half of the Baja California peninsula, north of the 28th parallel. The state is bordered on the west by the Pacific Ocean, on the east by Sonora, the U.S. State of Arizona, and the Gulf of California (also known as the Sea of Cortez), and on the south by Baja California Sur. Its northern limit is the U.S. state of California.

The state has a population of 2,844,469 (2005 census), and estimated 3,165,776 (June 2009) much more than the sparsely populated Baja California Sur to the south, and similar to San Diego County, California on its north. Over 75% of the population lives in the capital city, Mexicali, or in Ensenada and Tijuana. Other important cities include San Felipe, Rosarito and Tecate. The population of the state is composed of Mestizos, mostly immigrants from other parts of Mexico, and, as with most northern Mexican states, a large population of Mexicans of European ancestry, and also a large minority group of East Asian, Middle Eastern and indigenous descent. Additionally, there is a large immigrant population from the United States due to its proximity to San Diego and the cheaper cost of living compared to San Diego. There is also a significant population from Central America. Many immigrants moved to Baja California for a better quality of life and the number of higher paying jobs in comparison to the rest of Mexico and Latin America.

Baja California is the twelfth largest state by area in Mexico. Its geography ranges from beaches to forests and deserts. The backbone of the state is the Sierra de Baja California, where the Picacho del Diablo, the highest point of the peninsula, is located. This mountain range effectively divides the weather patterns in the state. In the northwest, the weather is semi-dry and mediterranean. In the narrow center, the weather changes to be more humid due to altitude. It is in this area where a few valleys can be found, such as the Valle de Guadalupe, the major wine producing area in Mexico. To the east of the mountain range, the Sonoran Desert dominates the landscape. In the south, the weather becomes drier and gives way to the Vizcaino Desert. The state is also home to numerous islands off both of its shores. In fact, the westernmost point in Mexico, the Guadalupe Island, is part of Baja California. The Coronado, Todos Santos and Cedros Islands are also on the Pacific Shore. On the Gulf of California, the biggest island is the Angel de la Guarda, separated from the peninsula by the deep and narrow Canal de Ballenas.