This book focuses on the rapidly growing research field of imperfect competition, asymmetric information, and other market imperfections in a macroeconomic context. It brings together leading researchers from the U.S. and Europe to examine the implications for macroeconomic policy of market imperfections in output, labor and financial markets. All the contributions are original, and include several general surveys and expository chapters that synthesize the larger literature, along with some state-of-the-art research at the frontier of the discipline. This is the first volume to focus exclusively on this literature. It should be a valuable resource for graduate students and researchers in macroeconomics.