Preliminary versions of most of the papers in this special issue of Annals of Economics and Statisticswere presented at the annual conference of the ADRES (Association pour le Développement de la Recherche en Economie et Statistiques). This conference, untitled ''New Developments in Social Choice and Welfare Theories - Conferences in Honor of Maurice Salles" took place at the University of Caen Basse Normandy from June 10th to 12th 2009. The articles collected here examine three aspects of modern social choice theory: the measure of inequality and welfare, the analysis of voting rules and voting behaviors, and Arrovian aggregation.