In this paper we describe what the IMF is and what it does. We consider its origins as the guardian of the Bretton Woods adjustable peg exchange rate system and financier of temporary current account deficits for advanced countries, to its present primary roles as development financier and crisis manager for the emerging world. We consider the externalities or market failures that the IMF is believed by many to correct and the public goods that the IMF provides. Critics of the IMF downplay the extent of market failure and the scope of public goods provided. They attach greater importance to market solutions. We consider their views as well. We conclude with a discussion of the case for reform in the light of historical experience.