'Can the values which individual members of society attach to different alternatives be aggregated into values for society as a whole, in a way that is both fair and theoretically sound? Is the majority principle a workable rule for making decisions? How should income inequality be measured? When and how can we compare the distribution of welfare in different societies?' So reads the 1998 Nobel citation by the Swedish Academy, acknowledging Amartya Sen's important contributions in welfare economics and particularly his work in Collective Choice and Social Welfare.Originally published in 1970, this classic study has been recognized for its ground-breaking role in integrating economics and ethics, and for its influence in opening up new areas of research in social choice. This expanded edition preserves the text of the original while presenting eleven new chapters of fresh arguments and results. Both the new and original chapters alternate between non-mathematical treatments of Sen's subjects accessible to all, and mathematical arguments and proofs. A new introduction gives a far-reaching, up-to-date overview of the subject of social choice.