This textbook presents a comprehensive treatment of the most important topics in monetary economics, focusing on the primary models monetary economists have employed to address topics in theory and policy. Striking a balance of insight, accessibility, and rigor, the book covers the basic theoretical approaches, shows how to do simulation work with the models, and discusses the full range of frictions that economists have studied to understand the impacts of monetary policy. For the fourth edition, every chapter has been revised to improve the exposition and to reflect recent research. The new edition offers an entirely new chapter on the effective lower bound on nominal interest rates, forward guidance policies, and quantitative and credit easing policies. Material on the basic new Keynesian model has been reorganized into a single chapter to provide a comprehensive analysis of the model and its policy implications. In addition, the chapter on the open economy now reflects the dominance of the new Keynesian approach. Other new material includes discussions of price adjustment, labor market frictions and unemployment, and moral hazard frictions among financial intermediaries. References and end-of-chapter problems allow readers to extend their knowledge of the topics covered. Monetary Theory and Policy continues to be the most comprehensive and up-to-date treatment of monetary economics, not only the leading text in the field but also the standard reference for academics and central bank researchers.