In Calculated Risk We have an excellent chart that shows how it has evolved Assets of the U.S. Federal Reserve, where we can see a very different visual strategy changes that the Fed has continued to fight recesion. observe, and after the summer of last year, the Fed decided to take the bull by the horns, and more than doubled the size of its balance sheet that step from just under one trillion dollars to clearly exceed two trillion dollars. At first, the Fed is dedicated to providing short-term liquidity to the banking system (blue zone), this did not work to revive the economy as banks kept the cash, but allowed to save the financial system so from February 2009, the Fed changed his strategy, it became more daring, he gave the little machine to print pieces of paper and began to buy Treasury Bonds (Red zone), and agency debt (are debt issued by entities such as Freddie Mac or Fannie Mae, and MBS (mortgage backed securities, the famous little packages of mortgage debt).