This special collection of Demographic Research – edited by Martin Dribe, Michel Oris, and Lucia Pozzi – is devoted to fertility differentials by socioeconomic status, to the relations between the socioeconomic stratification and the fertility decline, to the impact of changes in the labour market and/or the educational system on the transition processes. The collection is based on a selection of contributions to a workshop held in Alghero (Sardinia, Italy) in September 2012, organized by SIDES and the IUSSP Panel of Historical Demography. Covering Sweden, The Netherlands, Belgium, the regions of Scania (Sweden), Saguenay (Canada) and Utah (USA), as well as several urban and rural parishes in Italy, the contributions show no consistent evidence for the hypothesis that socioeconomic status was positively related to fertility before the demographic transition. There is more support for the idea that the upper and middle classes acted as forerunners in the transition, while especially farmers were late. After the transition fertility was lower in the middle class and especially among highly-educated women. The baby boom of the mid twentieth century changed this somewhat as fertility of the highly educated increased more than in other groups.