Corrado Bonifazi is director of research at theNational Research Council'sInstitute of Research on Population and Social Policy in Rome.Marek Okólski is chair in demography at the faculty of economic sciences and director of the Centre of Migration Research at the University of Warsaw.Jeannette Schoorl is senior researcher at the Netherlands Interdisciplinary Demographic Institute at The Hague.Patrick Simon is director of research at the National Demographic Institute in Paris.