Congestion effects in the location of workers and exports.

Summary This thesis aims to explain three major economic facts: excessive urban sprawl, unemployment dispersion, and trade hierarchy. In the first chapter, I construct and calibrate a simple labor market matching model in which the residential density of workers is endogenous. Using this analytical framework I show that the structure of the labor market creates significant excess sprawl. I identify the fact that firms compensate for the transportation costs of employees as the major source of this inefficiency. Finally, I point out that optimality can be restored if the government implements mileage compensation. The second chapter questions the fact that although it has been established that cities are characterized by a high dispersion of unemployment, segregation models remain the standard framework of urban and labor economics. In particular, I show that the classical model of this literature explains the dispersion of unemployment if the residential environment affects workers' preferences. In the third chapter, co-authored with Antoine Vatan, we show that whether firms follow a trade hierarchy depends very strongly on their experience as exporters. Then, we develop a simple and dynamic model that addresses the new empirical fact that we have highlighted. Namely, we show that this new fact can be explained by a trade-off between attractiveness and competition, the latter being present in any model of monopolistic competition with sequential exporting.