PIREDEU. Collaborative Project on "Providing an Infrastructure for Research on Electoral Democracy in the European Union", co-ordinated by the European University Institute and its Robert Schuman Centre for Advanced Studies.

EES. The European Election Studies are about electoral participation and voting behaviour in European Parliament elections. They are also concerned with the evolution of an EU political community and a European public sphere, with citizens' perceptions of and preferences about the EU political regime, and with their evaluations of EU political performance.
EES Data

CSES. The Comparative Study of Electoral Systems is a collaborative program of research among election study teams from around the world. Participating countries include a common module of survey questions in their post-election studies. The resulting data are deposited along with voting, demographic, district and macro variables. The studies are then merged into a single, free, public dataset for use in comparative study and cross-level analysis.

GESIS. GESIS – Leibniz-Institute for the Social Sciences is an institution that both conducts research and provides services, it renders substantial, nationally and internationally relevant research-based infrastructure services. GESIS stands for independence, reliability, quality, and competence in the fields of empirical social research, archiving, documentation, and information technology.
GESIS data

ICPSR. The Inter-University Consortium for Political and Social Research is an international consortium of about 700 academic institutions and research organizations. ICPSR provides leadership and training in data access, curation, and methods of analysis for the social science research community. It maintains a data archive of more than 500,000 files of research in the social sciences and hosts 16 specialized collections of data in education, aging, criminal justice, substance abuse, terrorism, and other fields.
ICPSR data