Amartya Sen was awarded the Nobel Memorial Prize in Economics in 1998 'for his contributions in welfare economics'. Although his primary academic appointments have been mostly in economics, Sen is also an important and influential social theorist and philosopher. His work on social choice theory is seminal, and his writings on poverty, famine, and development, as well his contributions to moral and political philosophy, are important and influential. Sen's views about the nature and primacy of liberty also make him a major contemporary liberal thinker. This volume of essays on aspects of Sen's work is aimed at a broad audience of readers interested in social theory, political philosophy, ethics, public policy, welfare economics, the theory of rational choice, poverty, and development. Written by a team of well-known experts, each chapter provides an overview of Sen's work in a particular area and a critical assessment of his contributions to the field.