The uncon ventional monetary policy measures adopted by the major central banks in the period since 2008 are discussed in this paper. We highlight some important differences between quan- titative easing and conventional monetary policy and then evaluate the mechanisms through which quantitative easing may propagate to financial markets and the real economy, drawing on perspec- tives from monetarist and New Keynesian theory. Additional measures, intended to supplement or strengthen the effects of pure quantitative easing, often termed unconventional unconventional monet- ary policy, are also assessed. In our discussion we relate the various articles in this issue to some of the key research questions posed in relation to unconventional monetary policy.