Total fertility rates have declined steadily in most OECD countries since the late 1960s. However, since the late 1990s there has been a fertility rebound in a large number of countries. Is this a temporary phenomenon, or a significant change in trend? To try and answer the question, it is important to establish the main drivers of fertility trends and how they have evolved recently. This chapter first reviews the mechanics involved: the postponement of family formation, smaller family sizes and the choice to remain childless. It then looks at the factors which may affect fertility decisions, including the direct cost of children (education and housing), and the indirect cost of foregone labour market opportunities. These vary with education and skill levels. The effects of fluctuations in economic growth are also considered. The chapter concludes with a discussion of the most promising policy initiatives to narrow the fertility gap.