This paper sets out a framework for classifying and thinking about unconventional monetary policies, highlighting how they can be viewed within the overall context of monetary policy implementation. The framework clarifies the differences among the various forms of unconventional monetary policy, provides a systematic characterization of the wide range of central bank responses to the recent crisis, helps to underscore the channels of transmission and identifies some of the main policy challenges. In the process, the paper also addresses a number of contentious analytical issues, notably the role of bank reserves and their inflationary consequences.