A central bank or monetary authority is an institution that manages the currency, money supply, and interest rates of a state or formal monetary union,and oversees their commercial banking system. In contrast to a commercial bank, a central bank possesses a monopoly on increasing the monetary base in the state, and also generally controls the printing/coining of the national currency,which serves as the state's legal tender.A central bank also acts as a lender of last resort to the banking sector during times of financial crisis. Most central banks also have supervisory and regulatory powers to ensure the solvency of member institutions, to prevent bank runs, and to discourage reckless or fraudulent behavior by member banks.