The U.S. Government Accountability Office (GAO) is an independent, nonpartisan agency that works for Congress. Often called the "congressional watchdog," GAO investigates how the federal government spends taxpayer dollars.
Their mission is to support the Congress in meeting its constitutional responsibilities and to help improve the performance and ensure the accountability of the federal government for the benefit of the American people.
Their work is done at the request of congressional committees or subcommittees or is mandated by public laws or committee reports. They also undertake research under the authority of the Comptroller General.