Based on lectures given as part of The Stone Lectures in Economics, this book discusses the problem of formulating monetary policy in practice, under the uncertain circumstances which characterize the real world. How should central banks set monetary policy? In which way should they take uncertainty into account when designing a monetary policy strategy? Should they respond to shocks aggressively or cautiously? These questions are discussed both with reference to the experience of the Bundesbank and of the European Central Bank and in relation to a simple stylized economic model.