State Route 188 (SR 188) is a two mile (3 km) route that connects State Route 94 with the Mexico – United States border. Its southern terminus is at the border near Tecate, Baja California and its northern terminus is near Tecate, California with SR 94. The route was assigned in the area in 1972, and has remained intact since.

State Route 188 or Tecate Road begins at the U.S.-Mexico border in the community of Tecate, Baja California; this border crossing handled roughly four percent of all traffic in between Baja California and California during 2008. The route progresses northward, passing through a large commercial district in Tecate, California. State Route 188 heads to an intersection with Thing Road, where it turns to the northeast and out of the commercial district. The route continues to the northeast, intersecting with Humphries Road, where the surroundings become highly undeveloped. State Route 188 continues to an intersection with State Route 94 a short distance out of Potrero, where the designation ends and right-of-way merges into State Route 94. The entire route is in the National Highway System, a network of roadways important to the country's economy, defense, and mobility.

The Tecate border crossing originally opened in 1932. The original alignment of SR 188, when routes where first assigned, was designated as Legislative Route 94. In the 1964 state highway renumbering, SR 188 was officially defined as "the south end of Fallen Leaf Lake to Route 89 near Camp Richardson"; this was later removed in 1965.

The current routing of State Route 188 was assigned in 1972. The route has remained virtually unchanged since. The Tecate border crossing expanded through the opening of the Tecate Commercial Vehicle Enforcement Facility, including truck scales; this was completed in 2008, with past expansions to the crossing having been completed in 2004 and 2005.

Improvements are being planned to connect the two ports of entry with a truck bypass to improve security; these are scheduled for completion by 2015.

Except where prefixed with a letter, postmiles were measured on the road as it was in 1964, and do not necessarily reflect current mileage. The entire route is in San Diego County.