The roles played by migration and family formation for economic growth have been well studied by economists. Yet these aspects have tended to be examined separately, without considering the interaction between family formation and migration. This project seeks to understand the extent of this interaction and how it shaped economic development in Western Europe. To address this question we intend to build and explore a new dataset combining data from online genealogical websites (Geni and Geneanet) with other sources, notably censuses. We aim at answering three questions: (Q1) How does family members' decision to migrate in search of better economic opportunities depend on the stage of family formation? (Q2) How were these decisions shaped by the major economic and social transformations that Europe experienced since the mid-17th century? (Q3) How did family formation and migration decisions contribute to economic growth in Western Europe? The first stage in the project will tackle an ambitious collection of data to build (and de-bias) our novel dataset. The latter will allow us to follow around 700 million Europeans over the period 1600 to 1940, providing rich information from their birth to their death that will identify both family dynamics and migration patterns. The data will first be used to analyze how fertility and migration decisions shaped each other, with a particular focus on the economic returns to migration and the implications for social mobility. The project will also consider the gender dimension of these questions, as gender norms are both an important determinant of family outcomes and a result of population dynamics and location choices. Results from these individual-level analyses will allow us to answer Q1 and Q2. We will then use structural estimations to understand how family migration affects long-run economic growth both at the local and aggregate levels, in order to answer our third research question, Q3.