Old Town Transit Center, also known as San Diego–Old Town station, or Old Town San Diego station, is an intermodal transportation station in the Old Town neighborhood of San Diego, California. It is served by Amtrak's Pacific Surfliner, the COASTER commuter rail service, and the San Diego Trolley, as well as numerous San Diego Metropolitan Transit System bus lines.

The station is located at the intersection of Rosecrans Street/Taylor Street and Pacific Highway, adjacent to Old Town San Diego State Historic Park and the freeway intersection of Interstate 5 and Interstate 8. It is also located about two miles southeast of SeaWorld San Diego and Mission Bay, providing access to the northernmost beaches in the city of San Diego. Free parking (Park & Ride) for up to 24-hours is available in the Transit Center lots.

Old Town Transit Center was built in the early 1990s, and the San Diego Trolley's North/South Line was extended here on June 16, 1996. In November 1997, the line, renamed the Blue Line, was extended into Mission Valley. When the Green Line service was introduced with the opening of the Mission Valley East extension on July 10, 2005, the Blue Line's northern terminus was pushed back to this station, which also served as the Green Line's western terminus. During a system redesign on September 2, 2012, as part of the Trolley Renewal Project, MTS extended the western terminus of the Green Line from this station to 12th & Imperial Bayside Terminal and shortened the Blue Line's northern terminus to America Plaza. The Special Event Line was eliminated; and instead, the Green Line added cars and offer more frequent service to the San Diego Convention Center, Petco Park, Snapdragon Stadium, and Viejas Arena when necessary.

As part of the Mid Coast Trolley Project, on November 21, 2021, the Blue Line returned to service the Old Town station. The Blue Line provides access to places such as the University of California, San Diego, Jacobs Medical Center, Westfield UTC, and the Mexico–United States border in San Ysidro.

The Old Town Transit Center hosts passenger trains operating on Amtrak's Pacific Surfliner intercity rail route and on the COASTER commuter rail service. Of the 22 weekday Amtrak Pacific Surfliner trains operating in San Diego, 18 of them stop at the Old Town Transit Center, though the Surfliner trains operating at Old Town do not offer checked luggage service, and stop at Old Town to board passengers (northbound trains) or detrain passengers (southbound trains) only, respectively.

Amtrak ridership at Old Town Transit Center has exploded between Fiscal Year 2011 and 2013. In Fiscal Year 2011, there were just 22,867 boardings and detrainings at Old Town (which was a 5.79% increase over Fiscal Year 2010). In Fiscal Year 2012, boardings and detrainings at Old Town rose to 61,118, a 167% increase over FY2011. As of Fiscal Year 2013, the Amtrak ridership figure has continued to rise, to 135,749 boardings and detrainings, a further 122% increase over FY2012. (There has been a corresponding decrease in Amtrak boardings at Santa Fe Depot in downtown San Diego over this same period, possibly indicating that some Amtrak boardings have been relocating from Santa Fe Depot to Old Town over the past two years.) Of the 74 California stations served by Amtrak, the Old Town Transit Center was the 25th-busiest in Fiscal Year 2013, boarding or detraining an average of approximately 372 passengers daily.

Old Town Transit Center is also a light rail station on the San Diego Trolley's Green Line. This station originally served as that line's terminus, until a system realignment in September 2012 extended the Green Line though Old Town to downtown San Diego.

The Trolley's Mid-Coast extension that was completed in November 2021 extends to serve the University City area.

Old Town also operates as a bus transit center for San Diego Metropolitan Transit System's routes 8, 9, 10, 28, 30, 35, 44, 83, 88, and 105. There is an underground pedestrian tunnel linking bus terminals on both sides of the station with the trolley/train areas.

The station is also served by San Diego International Airport's San Diego Flyer shuttle which operates every 20 to 30 minutes between the Old Town Transit Center, Terminal 1 and Terminal 2. The station also sees service from UC San Diego's Triton Transit Hillcrest Express, which connects passengers with the UC San Diego Medical Center, Hillcrest, University of San Diego shuttles, and FlixBus intercity motorcoaches.

There are four tracks; two tracks are designated for the San Diego Trolley services, while the other two tracks are used for COASTER, Amtrak, and BNSF freight service.

Bus bays	MTS Access,  San Diego Flyer shuttle, Hillcrest Express shuttle
Bus bays	Store, MTS bus routes 44, 83, 88 & 105
Side platform
Track 1 Northbound	← Blue Line toward UTC (Tecolote Road) ← Green Line toward El Cajon (Morena/Linda Vista)
Island platform
Track 2 Southbound	→ Blue Line toward San Ysidro (Washington Street) → → Green Line toward 12th & Imperial (Washington Street) →
Island platform
Track 3 Southbound	Coaster toward San Diego (San Diego)→ Pacific Surfliner toward San Diego (San Diego) → BNSF freight service →
Track 4 Northbound	← Coaster toward Oceanside (Sorrento Valley) ← Pacific Surfliner toward San Luis Obispo (Solana Beach) ← BNSF freight service
Side platform
Bus bays	MTS bus routes 8, 9 & 28
Bus bays	MTS bus routes 30 & 35
Parking lot	Parking, bus bay for MTS bus route 10
Pacific Highway	Bus bay for  San Diego Flyer shuttle

• List of San Diego Trolley stations

• San Diego, CA–Old Town – Amtrak
• San Diego, CA–Old Town – Station history at Great American Stations (Amtrak)
• COASTER Stations
• Old Town Transit Center – SDMTS
• Old Town San Diego Amtrak Station – USA RailGuide (TrainWeb)
• Old Town San Diego State Historic Park (California State Parks)