The Orange Line is a Bay Area Rapid Transit (BART) line in the San Francisco Bay Area that runs between Berryessa/North San José station and Richmond station. It has 21 stations in San Jose, Milpitas, Fremont, Union City, Hayward, San Leandro, Oakland, Berkeley, El Cerrito, and Richmond. It is the only one of the five primary BART services that does not run through the Transbay Tube to San Francisco; however, it shares tracks with the four other primary services in the East Bay.

The Orange Line was the first BART line to open. Initial services between MacArthur and Fremont stations began on September 11, 1972, with full service extending to Richmond beginning on January 29, 1973.

The line would not see any major changes for another 45 years, until the start of the Silicon Valley BART extension. The first phase of the project extended the line to Warm Springs/South Fremont station in March 2017, the second phase added Berryessa/North San José and Milpitas stations in June 2020.

The Orange Line runs primarily north-south through the East Bay. It uses the R-Line between Richmond station and just north of MacArthur station, the K-Line between MacArthur and the Oakland Wye, the A-Line between the Wye and Fremont station, and the S-Line between Fremont and Berryessa/North San José station. Most sections are at-grade or elevated; the line runs through tunnels in downtown Berkeley, downtown Oakland, and under Lake Elizabeth.

Station	Jurisdiction	County	Opened	Other BART lines
Richmond	Richmond	Contra Costa	January 29, 1973	R  Red Line
El Cerrito del Norte	El Cerrito
El Cerrito Plaza
North Berkeley	Berkeley	Alameda
Downtown Berkeley
Ashby
MacArthur	Oakland		September 11, 1972	R  Red Line  Y  Yellow Line
19th Street Oakland
12th Street Oakland City Center
Lake Merritt				B  Blue Line  G  Green Line
Fruitvale
Coliseum				OAK  Oakland Airport Connector  B  Blue Line  G  Green Line
San Leandro	San Leandro			B  Blue Line  G  Green Line
Bay Fair
Hayward	Hayward			G  Green Line
South Hayward
Union City	Union City
Fremont	Fremont
Warm Springs/​South Fremont			March 25, 2017
Milpitas	Milpitas	Santa Clara	June 13, 2020
Berryessa/​North San José	San Jose