Thesis: A key characteristic of the process of economic development is the shrinking spatial mismatch between economic activity and population. This thesis analyzes what happens when this spatial mismatch is reduced, as people’s places of residence and work or the geographical distribution of economic activity is altered. Chapter I deals with the relationship between international migrants and their households of origin. It sheds light on the importance for remittances and investments of migrants' beliefs and the information asymmetry between remittance senders and recipients that distance aggravates. Chapter II explores the transformation of the receiving economy due to an influx of rural-to-urban migrants in China. It first quantifies the effect of immigrants on the labor market at destination, and then investigates their impact on the reallocation of production factors and factor-market constraints faced by urban firms. Chapter III focuses on the long-term impact of a large industrialization plan in China. It reveals a reversal pattern due to the distortions in local labor markets induced by the presence of big plants. It highlights the role of migration in overcoming such imperfections and in bringing about the later stage of structural transformation—from heavy industry to consumption goods and services.