The Sacramento River is an important river of Northern and Central California in the United States. The state's largest river by discharge, it rises in the Klamath Mountains and flows south for over 400 miles (640 km) before reaching Suisun Bay, an arm of San Francisco Bay, and thence the Pacific Ocean. The Sacramento drains an area of about 27,500 square miles (71,000 km²) in the northern half of the state, mostly within a region bounded by the Coast Ranges and Sierra Nevada known as the Sacramento Valley. Its extensive watershed also reaches to the volcanic plateaus of Northeastern California. Historically, its watershed has reached farther, as far north as south-central Oregon where the now, primarily, endorheic (closed) Goose Lake rarely experiences southerly outflow into the Pit River, the most northerly tributary of the Sacramento.

The Sacramento has been an important transportation route since the time of the region's first inhabitants, who settled in the river valley about 12,000 years ago. Hundreds of tribes sharing regional customs and traditions inhabited the Sacramento Valley, though they received little disturbance upon the arrival of Europeans in the 1700s. One of these early explorers, Gabriel Moraga, gave the river the Spanish name, Rio de los Sacramentos, later shortened and anglicized into Sacramento. The Sacramento's waters were once abundant in fish and other aquatic creatures, notably one of the southernmost runs of chinook salmon in North America. The original natives of the Sacramento Valley drew upon the vast natural resources of the watershed, which had one of the densest American Indian populations of California.