The Inland Empire–Orange County (IEOC) Line is a commuter rail line run by Metrolink in Southern California. It runs from San Bernardino through Orange County to Oceanside in northern San Diego County. When the line opened it became the first Metrolink line not to serve Union Station in Los Angeles nor cross the Los Angeles River and was the only line until the Arrow service opened in October 2022. The line was also the first suburb-to-suburb commuter rail line in the United States.

Metrolink is a commuter rail system in Southern California, serving Los Angeles, Orange, Riverside, San Bernardino, and Ventura counties, as well as to Oceanside in San Diego County. The system consists of eight lines and 69 stations operating on 545.6 miles (878.1 km) of track. Arrow is operated under a contract with the San Bernardino County Transportation Authority (SBCTA).