Inspired by the work of Ron Lesthaeghe, retired professor of demography and social science research methodology, this collection is also based on the 'Demographic Challenges for the 21st Century: A State of the Art in Demography" conference. During Ron Lesthaeghe's tenure, he established himself as a scholar, publishing influential work that changed the face of demography. His research was in the various subfields of demography, populations of Europe and of sub-Saharan Africa, cultural change in Europe, and ethnic minority studies. This book offers tributes to his contribution, from leading demographers.