U.S. Route 101 (US 101) is a major north–south United States Numbered Highway, stretching from Los Angeles, California, to Tumwater, Washington. The California portion of US 101 is one of the last remaining and longest U.S. Routes still active in the state, and the longest highway of any kind in California. US 101 was also one of the original national routes established in 1926. Significant portions of US 101 between the Los Angeles area and the San Francisco Bay Area follow El Camino Real, the commemorative route connecting the former Alta California's 21 missions.

El Camino Real is a 600-mile (965-kilometer) commemorative route connecting the 21 Spanish missions in California, along with a number of sub-missions, four presidios, and three pueblos. Historically associated with the Calle Real which terminates in Mexico City, as the former capital of New Spain and the seat of royal power for Las Californias, its southern end in the modern U.S. state of California is at Mission San Diego de Alcalá and its northern terminus is at Mission San Francisco Solano.