The Baja California peninsula (Lower California), is a peninsula in northwestern Mexico. Its land mass separates the Pacific Ocean from the Gulf of California. The Peninsula extends 1247 km from Mexicali, Baja California in the north to Cabo San Lucas, Baja California Sur in the south. It ranges for 40 km at its narrowest to 320 km at its widest point and has approximately 3000 km of coastline and approximately 65 islands. The total area of the Baja California Peninsula is 143390 sqkm.

The Peninsula is separated from mainland Mexico by the Gulf of California and the Colorado River, though on the Colorado there are bridges to the state of Sonora. There are four main desert areas on the peninsula: the San Felipe Desert, the Central Coast Desert, the Vizcaíno Desert and the Magdalena Plain Desert.