Amartya Sen has made deep and lasting contributions to the academic disciplines of economics, philosophy, and the social sciences more broadly. He has engaged in policy dialogue and public debate, advancing the cause of a human development focused policy agenda, and a tolerant and democraticpolity. This argumentative Indian has made the case for the poorest of the poor, and for plurality in cultural perspective. It is not surprising that he has won the highest awards, ranging from the Nobel Prize in Economics to the Bharat Ratna, India's highest civilian honor. This public recognitionhas gone hand in hand with the affection and admiration that Amartya's friends and students hold for him. This volume of essays, written in honor of his 75th birthday by his students and peers, covers the range of contributions that Sen has made to knowledge. They are written by some of the world's leading economists, philosophers and social scientists, and address topics such as ethics, welfareeconomics, poverty, gender, human development, society and politics. This first volume covers the topics of Ethics, Normative Economics and Welfare; Agency, Aggregation and Social Choice; Poverty, Capabilities and Measurement; and Identity, Collective Action and Public Economics. It is a fittingtribute to Sen's own contributions to the discourse on Ethics, Welfare and Measurement.