The Washington Metropolitan Area Transit Authority (WMATA), Fairfax County, Loudoun County, Town of Herndon and the Metropolitan Washington Airports Authority (MWAA) are partners in this 23-mile transit extension in the rapidly growing Dulles Corridor in Fairfax and Loudoun Counties, Virginia.

The Dulles Corridor is home to several of the Washington, D.C., metropolitan region's most dynamic and rapidly growing activity centers, including Tysons Corner, the Reston-Herndon area, Dulles International Airport and the emerging activity centers in eastern Loudoun County. Tysons Corner is the state's largest job center. Reston/Herndon is the second.

The purpose of Dulles Metrorail is to provide high-quality, high-capacity transit service in the Dulles Corridor and to provide a transit connection between the corridor and downtown Washington. The new Metrorail service results in travel time savings and expands the reach of the existing regional rail system, and offers a viable alternative to automobile travel and supports future development along the corridor.

A Draft Environmental Impact Statement (EIS) for the project was completed in June 2002. This Draft EIS evaluated several alternatives, including three Bus Rapid Transit (BRT) options, a combined BRT/Metrorail alternative and a full Metrorail extension. Public hearings on the Draft EIS were held in July 2002. Based on extensive public comments and input from local jurisdictions, the full extension of Metrorail was recommended as preferred option or Locally Preferred Alternative (LPA).

The Dulles Corridor Metrorail Project was approved by the WMATA Board of Directors in November 2002 and the Commonwealth Transportation Board (CTB) in December 2002. The Project was also endorsed by the Fairfax County, Loudoun County and MWAA Boards.

Following these approvals, a Final EIS was published in December 2004 and the Federal Transit Administration issued its Record of Decision approving the environmental process in March 2005.

Phase 1 of the project now extends the existing Metrorail system from the East Falls Church Station on the Orange Line in Fairfax County through Tysons Corner to Wiehle Avenue on the eastern edge of Reston. Phase 2 extends from Reston west to Washington Dulles International Airport and beyond to Route 772/Ryan Road in Loudoun County.

Service on the new Metrorail line will continue from stations in Tysons Corner and the Dulles Corridor onto the existing Orange Line tracks and serve the Orange Line stations from East Falls Church through Arlington County and into Washington, D.C. to the Stadium-Armory Station. From that point, trains follow the existing Blue Line tracks to Largo, Md. The decision was made in 2013 to continue the trains to Largo rather than end service at Stadium Armory.