This book presents important aspects of the New-Keynesian theory of monetary policy and its implications for the practical decision making of central bankers today. It brings together several new research contributions that were presented at the scientific symposium on the occasion of the award of the Deutsche Bank Prize in Financial Economics 2007 to Professor Michael Woodford of Columbia University. Woodford received this prize according to the jury in recognition of his fundamental contributions to the theory and practical analysis of monetary policy. The prize jury included Gunter Franke, Michael Haliassos, Otmar Issing, Jan Krahnen, Patrick Lane, Lucrezia Reichlin, Reinhardt Schmidt, Lars Svensson, Norbert Walter and Volker Wieland. The first part on "The New-Keynesian Approach to Understanding the Economy" contains two chapters written by Bennett McCallum and Jordi Gali, respectively. McCallum provides an exposition of key elements of the New-Keynesian approach to monetary policy analysis and an appreciation of Woodford's contributions. Gali further develops several key lessons of this approach and points out important new directions for further research.