The term quantitative easing (QE) describes a monetary policy used by some central banks to increase the supply of money by increasing the excess reserves of the banking system. This policy is usually invoked when the normal methods to control the money supply have failed, i.e the bank interest rate, discount rate and/or interbank interest rate are either at, or close to, zero.

A central bank implements QE by first crediting its own account with money it creates ex nihilo ("out of nothing"). It then purchases financial assets, including government bonds, agency debt, mortgage-backed securities and corporate bonds, from banks and other financial institutions in a process referred to as open market operations.