The project is about subjective well-being (SWB) and demographic behaviour, with a particular focus on fertility in advanced societies, across time and space. The project is motivated by the fact that European and other advanced industrialized countries have for decades experienced below-replacement fertility levels, which are now posing dramatic challenges to ageing population structures. Cross-sectional and temporal variations in fertility remains an unsolved puzzle for current theories of below-replacement fertility. The argument put forward in this project is that SWB may be the missing link in the understanding of why countries differ so significantly in fertility.The project has a strong interdisciplinary perspective with the following aims:- to advance the understanding of the complex link between SWB and fertility, bringing together a longitudinal perspective with a comparative perspective;- to examine the role of policies, welfare provision and social norms operating at different levels, addressing possible policy measures that would improve the SWB of individuals and couples, leading eventually to increased fertility- to communicate findings and stimulate the academic and policy debate on how SWB matters for fertility, highlighting the relevance of SWB for future data collection efforts and the potential use of SWB for fertility projections;The project relies upon secondary data sources, both longitudinal and comparative in nature. The assessment of SWB and fertility requires statements about causality and interactions with the relevant context. By explicitly addressing the linkages between SWB and fertility in a systematic way, the project will address an important gap in the literature, helping to modify mainstream theoretical frameworks for the understanding fertility variation and contributing to the creation of a new paradigm of post-transitional fertility theory