Andreu Mas-Colell has been doing pioneering work using differential topology in the analysis of general equilibrium. This work is regarded as outstanding and one of the major contributions to the development of rigorous economic theory in the last twenty years. The articles he has written have been difficult and technically demanding. In this book he brings this work together to show its scope and its power. He presents the analysis in a way which makes it accessible to the broader range of economic theorists and advanced students. This book has been long awaited as a seminal contribution to the subject.