This study analyzes the variation of legal migration flows between Mexico and the United States (U.S.) from the entry into force of the North American Free Trade Agreement (NAFTA). As a product of the asymmetry in the size of the U.S., Canadian and Mexican economies, migration flows, both from Canada and Mexico, have the U.S. as their primary destination. This essay focuses primarily on legal economic migration linked to highly skilled jobs, particularly on migrant workers with L-type visas, for intercompany transfers, and TN-type visas, for professionals. Both of them created since NAFTA. The research hypothesis of this study is that, since the entry into force of NAFTA, legal migration flows have increased as a result of the intensification of the economic relationship between the two countries, particularly as a result of the intensification of free trade.