The majority of economists, would admit that money is powerful and that changes in money will impact the economy, to some extent and most of the time. Monetary theory analyzes and determines how changes in the supply of money affect the economy. The collection of policies that use monetary tools is known as monetary policy. The main monetary authority of a country is its central bank. In the United States it is called the Federal Reserve Bank System (Fed), which is a federation of 12 Federal Reserve Banks.