Westlake/MacArthur Park station is an underground rapid transit, known locally as a subway, station on the B Line and D Line of the Los Angeles Metro Rail system. The station is located near the intersection of Wilshire Boulevard and Alvarado Street in the Los Angeles neighborhood of Westlake, after which the station is named, along with MacArthur Park, which is located across the street. Unlike most of Metro's other underground stations, which are built directly under a street, the Westlake/MacArthur Park platform is located south of Wilshire Boulevard and between 7th Street. This design allowed a train storage area to be built under MacArthur Park, and necessitated draining the lake for several years to excavate and build the tracks.

The B Line is a fully underground 14.7 mi (23.7 km) rapid transit line operating in Los Angeles, running between North Hollywood and Downtown Los Angeles. It is one of six lines in the Los Angeles Metro Rail system, operated by the Los Angeles County Metropolitan Transportation Authority. Built in four stages between 1986 and 2000, the line cost $4.5 billion.