Baja California Sur, literally "South Lower California", officially the Free and Sovereign State of Baja California Sur, is the second-smallest Mexican state by population and the 31st admitted state of the 31 states which, with the Mexico City, make up the 32 Federal Entities of Mexico.

Before becoming a state on October 8, 1974, the area was known as the South Territory of Baja California (El Territorio Sur de Baja California). It has an area of 73,909 km2 (28,536 sq mi), or 3.57% of the land mass of Mexico, and occupies the southern half of the Baja California Peninsula, south of the 28th parallel, plus the uninhabited Rocas Alijos in the Pacific Ocean. It is bordered to the north by the state of Baja California, to the west by the Pacific Ocean, and to the east by the Gulf of California, or the "Sea of Cortés". The state has maritime borders with Sonora and Sinaloa to the east, across the Gulf of California.

The state is home to the tourist resorts of Cabo San Lucas and San José del Cabo. Its largest city and capital is La Paz.