Professor David Coleman from Dept of Social Policy, University of Oxford, gives a talk from his "Demographic Trends and Problems of the Modern World" series talking about the 'Second Demographic Transition'. The early 20th century was a time of very low divorce rates and of births outside marriage. Couples married late and many never married. In Western Europe, and the English-speaking world, all that changed after the 1960s; Cohabitation, divorce, births outside marriage made families much more diverse. The theory of the 'Second demographic transition' explains these trends as the result of new individual autonomy in a society now highly educated, secular and prosperous, with welfare arrangements supporting a variety of family types. As prosperity and education become globalised, the theory predicts that this diversity of behaviour will also be globalised. The lecture examines its scope and sustainability.