This report tries to explain observed changes in fertility rates across OECD countries, with an emphasis on socio-economic considerations. It aims to extend the understanding of fertility-related behaviours in different ways: first, by explaining recent developments in fertility rates and their relationships to other social drivers; second, by developing and testing new and expanded models to explain the cross-country variation in fertility rates due to labour markets, social and fiscal policies, and individual characteristics; third, by exploring which polices, through their effects on particular variables at micro and macro levels, have the biggest effect on fertility rates.