This project will address key issues related to fertility and reproduction in 21st century Europe and their implications. We aim to expand our knowledge of contemporary reproductive behaviour, critically assess theoretical perspectives on fertility, develop new indicators for analyzing and projecting fertility and improve our understanding of fertility intentions.Combining detailed databases, especially the expanding Human Fertility Database, as well as surveys, and theoretical perspectives, the research team will study contemporary fertility trends and their explanations. An emphasis will be put on analyzing and explaining very low fertility that became a matter of public concern in some countries.We will review and confront the existing theories of fertility and examine their validity and premises at different levels of explanation. We will look how and under which circumstances they can illuminate observed fertility trends as well as the reversals in correlation between selected aggregate level-level indicators (female labour force participation, GDP level, marriage rates, etc.) and fertility.Specific attention will be paid to studying systematically fertility intentions and desires of men and women in different settings and populations. Here the key issue is whether and why a systematic disagreement between intended and realized fertility exists at an aggregate level.Finally, we aim to elaborate the indicators of fertility and population replacement. These will be used to assess long-term implications of contemporary fertility and migration patterns for population change and composition in different regions of Europe.