The Washington Metro, often abbreviated as the Metro and formally the Metrorail, is a rapid transit system serving the Washington metropolitan area of the United States. It is administered by the Washington Metropolitan Area Transit Authority (WMATA), which also operates the Metrobus service under the Metro name. Opened in 1976, the network now includes six lines, 98 stations, and 129 miles (208 km) of route.

Rapid transit or mass rapid transit (MRT), also known as metro, is a type of high-capacity public transport that is generally built in urban areas. A rapid transit system that primarily or traditionally runs below the surface may be called a subway, tube, or underground. Unlike buses or trams, rapid transit systems are railways, usually electric, that operate on an exclusive right-of-way, which cannot be accessed by pedestrians or other vehicles. They are often grade-separated in tunnels or on elevated railways.