Arrow is a hybrid rail (light rail with some features similar to commuter rail) service in San Bernardino County, California, United States. Opened on October 24, 2022, the line runs from the San Bernardino Transit Center in Downtown San Bernardino in the west to the University of Redlands in Redlands in the east.

The line was planned and constructed by the San Bernardino County Transportation Authority as the Redlands Passenger Rail Project and is operated under contract by Metrolink, which integrates Arrow into its commuter rail system, making it the only line in the entire Metrolink system to be entirely in San Bernardino County and also became the second line not to serve Los Angeles Union Station nor cross the Los Angeles River since the opening of the Inland Empire–Orange County Line in October 1995. This is the first and only Metrolink line to utilize completely different rolling stock than the rest of the system.

The 9-mile (14 km) route uses a former Atchison, Topeka and Santa Fe Railway line. While mostly a single track line, 2 miles (3.2 km) of double track were constructed in the middle of the route to allow vehicles to pass each other. Low-volume freight service by BNSF Railway uses the route during overnight hours when Arrow service is not running for a few customers located on the portion of the line just west of San Bernardino–Tippecanoe station.

Arrow trains operate daily. On weekdays, service runs between approximately 4 am and 11 pm, with 30-minute frequencies during the early morning and evening peak periods and hourly service at other times. On weekends, trains operate between about 7:30 pm and 10 pm at hourly intervals, with three one-hour gaps in service in the morning, afternoon, and evening.

Between 10 and 11 pm on weekend nights, trains run every 30 minutes between Redlands–Downtown and Redlands–University.

Most trip schedules are coordinated to allow relatively short connection times with San Bernardino Line trains at San Bernardino Transit Center for trips to and from Los Angeles.

From west to east, the line starts at the San Bernardino Transit Center (also called San Bernardino–Downtown station), where passengers can transfer to several local and regional bus routes, Metrolink trains and the sbX bus rapid transit line, the line then makes stops at San Bernardino–Tippecanoe station, crosses under Interstate 10 and enters Redlands reaching the Redlands–Esri station, after that trains enter central Redlands serving Redlands–Downtown station, built alongside the historic Redlands Santa Fe Depot, before reaching its final stop, Redlands–University station at the University of Redlands.

FLIRT diesel multiple units (DMUs) built by Stadler Rail were selected for service on the Arrow line under a $31.4 million contract.