He was president of the International Political Science Association from 1970 to 1973, president of the International Social Science Council (ISSC), which was founded by UNESCO, from 1973 to 1977, vice-president of the International Sociological Association from 1966 to 1970, and chairman (from 1970 to 1976) and co-founder of the European Consortium for Political Research (ECPR).
Han var præsident for International Political Science Association fra 1970 til 1973, præsident for UNESCOs International Social Science Council (1973-77), vicepræsident forInternational Sociological Association fra 1966 til 1970, og bestyrelsesformand (fra 1970 til 1976) og medstifter af European Consortium for Political Research.