A central bank, reserve bank, or monetary authority is an institution that manages a state's currency, money supply, and interest rates. Central banks also usually oversee the commercial banking system of their respective countries. In contrast to a commercial bank, a central bank possesses a monopoly on increasing the monetary base in the state, and usually also prints the national currency, which usually serves as the state's legal tender. Central banks also act as a "lender of last resort" to the banking sector during times of financial crisis. Most central banks usually also have supervisory and regulatory powers to ensure the solvency of member institutions, prevent bank runs, and prevent reckless or fraudulent behavior by member banks.