The Federal Reserve
The Federal Reserve System is the central bank of the United States. It is an autonomous and private entity that controls the organizational structure in which a government agency, known as the Board of Governors, based in Washington DC participates. Thus, some consider this as the public aspect of the system and the 12 Reserve Banks of all the country, the private aspect. It is in charge of guarding part of the reserves of the "member banks" of the United States: the federal ones, and the associated state voluntarily.