An introduction to the way that central banks implement monetary policy through market operations. It explains monetary policy operations in normal times, reviews the basic mechanics of financial crises, and explains what central banks need to do to fulfil their monetary policy and financial stability mandates when markets and banks are impaired. Ulrich Bindseil's book provides a consistent framework to understand central bank action, including the related trade-offs and dilemmas. It is both principle-based and deeply rooted in the ECB experience in the European crisis. It is a must read for central bankers, in sunny and in rainy days.