Essays on migration and productivity.

Summary This thesis examines the interaction between migration and productivity from different perspectives across three countries and time periods. Specifically, I study the labor market mobility benefits of migrants during economic downturns, the productivity gains from migrant mobility during a country's post-war reconstruction, and the gains associated with higher population concentration in large urban areas. I address these topics both theoretically and empirically, using rich confidential social security data from Spain, Germany, and Turkey, using various panel data techniques as well as historical instruments to estimate causal relationships. The results of these studies address many issues that are of interest to both academia and policymakers, but about which little is yet known. This dissertation aims to contribute to improving our knowledge on issues that will remain relevant in the near future.