Foothill Transit is a public transit agency that is government funded by 22 member cities in the San Gabriel and Pomona valleys. It operates a fixed-route bus public transit service in the San Gabriel Valley region of eastern Los Angeles County, California, United States, as well as a rapid bus route to and from downtown Los Angeles from the El Monte Busway, and a few of its local routes reach the far northern and western edge cities of neighboring Orange and San Bernardino counties, respectively. In 2023, the system had a ridership of 7,859,200, or about 27,500 per weekday as of the fourth quarter of 2023.

The San Gabriel Valley, often referred to by its initials as SGV, is one of the principal valleys of Southern California, with the city of Los Angeles directly bordering it to the west, and occupying the vast majority of the southeastern part of Los Angeles County. Surrounding landforms and other features include the following:the San Gabriel Mountains to the north; the San Rafael Hills to the west, with the Los Angeles Basin beyond; the Crescenta Valley to the northwest; the Puente Hills to the south, with the coastal plain of Orange County beyond; the Chino Hills and San Jose Hills to the east, with the Pomona Valley and Inland Empire beyond; and the city limits of Los Angeles, bordering its western edge.