The Federal Reserve System, the central bank of the United States, buys and sells securities as it conducts open market operations or other programs. The Fed creates or "prints" money to purchase these securities, increasing the money supply when it does so. If at some point it begins to sell these securities, the money supply can be reduced. The "Federal Reserve Balance Sheet" includes these purchased securities and smaller amounts of other securities. As of March 2013, the total of these two types (Treasury $1.78 trillion and MBS of $1.09 trillion) was $2.87 trillion, up from $476 billion at the start of 2009. Prior to 2009, the Fed did not purchase MBS. The purchases were begun as an emergency measure to stabilize the housing market in 2009. The Federal Reserve releases details of its balance sheet in its weekly H.4.1 statistical release. As of March 21, 2013 the balance sheet included $3.25 trillion of securities.^[1] The data for the chart comes from the indicated FRED database series in the chart (TREAST and MBST).