Emmanuel Saez, 36, a public economics expert teaching at the University of California at Berkeley, was awarded the 2009 John Bates Clark Medal last week. Nobody has done more to describe the broad changes in income distribution in the United States that have taken place during the last ninety years.
"[Saez's] work attacks policy questions from both theoretical and empirical perspectives, on the one hand refining the theory in ways that link the characteristics of optimal policy to measurable aspects of the economy and of behavior, while on the other hand undertaking careful and creative empirical studies designed to fill the gaps in measurement identified by the theory. Through a collection of interrelated papers, he has brought the theory of taxation closer to practical policy making, and has helped to lead a resurgence of academic interest in taxation."
Also see here.