Quantitative easing (QE) is an unconventional monetary policy used by central banks to stimulate the economy when standard monetary policy has become ineffective. A central bank implements quantitative easing by buying specified amounts of financial assets from commercial banks and other private institutions, thus increasing the monetary base and lowering the yield on those financial assets. This is distinguished from the more usual policy of buying or selling short term government bonds in order to keep interbank interest rates at a specified target value.
Expansionary monetary policy to stimulate the economy typically involves the central bank buying short-term government bonds in order to lower short-term market interest rates. However, when short-term interest rates have reached or are close to reaching zero, this method can no longer work. Quantitative easing may then be used by monetary authorities to further stimulate the economy by purchasing assets of longer maturity than short-term government bonds, and thereby lowering longer-term interest rates further out on the yield curve. Quantitative easing raises the prices of the financial assets bought, which lowers their yield.
Quantitative easing can be used to help ensure that inflation does not fall below target. Risks include the policy being more effective than intended in acting against deflation (leading to higher inflation in the longer term, due to increased money supply), or not being effective enough if banks do not lend out the additional reserves. According to the IMF and various other economists, quantitative easing undertaken since the global financial crisis of 2007–08 has mitigated some of the adverse effects of the crisis.