In this article,Nobel Prize Laureate Joseph Stiglitz argues that the standard macro-economic paradigm has failed not only to predict the crisis but also to provide insights into the design of a regulatory framework that would make a recurrence less likely.He points out that many of the underlying assumptions of the standard paradigm always seemed implausible and many of its predictions,such as those concing the micro-economic behavior of the constituents (firms and households),are inconsistent with the empirical evidence.He then identifies a number of key modeling challenges,what he views as key ingredients that have to be incorporated in any model that is going to describe economic fluctuations or be the basis of a well-designed regulatory or monetary framework.