The United States Government Manual is the official handbook that describes the activities and programs of the three branches of the federal government (executive, legislative, and judicial), agencies and quasi-official agencies, and international organizations of which the U.S. is a member. The manual includes descriptions and organizational charts of each component, and identifies key employees. It is updated annual as a special edition of the Federal Register.
CRS Reports are created by the Congressional Research Service as summaries of a variety of topics relevant to law-making activities.
GAO Reports are produced by the Government Accountability Office. The GAO is a government "watchdog" that investigates how agencies spend tax dollars.