1 THE BABY BOOM: NEW PERSPECTIVES AND NEW ISSUES. A research initiative David Reher 1,3 , Miguel Requena 2,3 , María Sánchez-Dominguez 1,3 and Alberto Sanz-Gimeno 1,3 1 Universidad Complutense de Madrid - UCM 2 Universidad Nacional de Educación a Distancia - UNED 3 Grupo de Estudios Población y Sociedad – GEPS PRELIMINARY VERSION, DO NOT QUOTE Introduction The baby boom is generally thought of as a period of demographic effervescence that affected the developed nations of the world, especially for most of those participating in World War II, and took place between the mid- to late-1940s and the late-1960s or early-1970s. During this period the dynamics of reproduction changed with marriage rates accelerating, total fertility rising (or at least stable) and the number of births increasing substantially. The baby boom put an end to the decades-long decline in fertility dating back to the nineteenth century, though actual changes TFRs in different societies at mid-century varied widely. The baby boom came to an end with the advent of widespread and modern methods of birth control, rapidly declining fertility, lower marriage rates and a profound change in the prevailing attitudes towards the family and reproduction. There is a large literature on the baby boom and its causes, but no definitive explanations exist (see Byerly [1985] for a literature review on the US experience; see also van Bavel and Reher [2012] for a review of current explanations). Much of this literature evaluates the processes involved and situates it within the perspective of long term population change (Chesnais, 1992; Sardon, 2006; Russell, 2006; Macunovich, 2002; Emeka, 2006; Romaniuk, 1984; Owram, 1996). Most explanations emphasize the importance of the return home of soldiers participating WWII, a period of economic growth that affected many countries in the aftermath of the war, a period in which relatively small cohorts had ample economic and social expectations before them, and a period of general optimism reinforced by cultural contexts in which large families were held up as a socially desirable goal for all. There