The company came about at the turn of the 20th century when it consolidated a handful of streetcar lines. It began as the San Francisco, Oakland, and San Jose Railway in 1902 and services began a year later. The general manager of the company created a new form of map in the style of an old-fashioned key, with three handle loops covering the cities of Berkeley, Piedmont, and Oakland. This became known as the key route, and the company became known as Key System.
The Key System's famed commuter train system was dismantled in 1958 after many years of declining ridership. The last run was on April 20, 1958. In 1960, the newly formed publicly owned AC Transit took over the Key System's facilities.