It is the role of the federal reserve, Known simply as the Fed, to control the supply of money in the U.S. throught its system of twelve regional federal Reserve Banks, each with its own federal reserve district Bank, Many commercial banks belong to the Federal Reserve system and as members must follow the Fed's reserve requirements, a ruling by the Fed on the percentage of deposits that a member bank must keep either in its own vaults or on deposit at the fed. If the fed wants to change the money supply,it can change reserve requirements to member banks; for example, an increase in the percentage of deposits required to be kept on hand would reduce the available money supply.