Discussions of questions at the cutting edge of macroeconomics that are central to contemporary policy debates, analyzing both current macroeconomic issues and recent theoretical advances.This 21st edition of the NBER Macroeconomics Annual treats many questions at the cutting edge of macroeconomics that are central to current policy debates. The first four papers and discussions focus on such current macroeconomic issues as how structural-vector-autoregressions help identify sources of business cycle fluctuations and the evolution of U.S. macroeconomic policies. The last two papers analyze theoretical developments in optimal taxation policy and equilibrium yield curves.