Abstract
Interpretations of the “alien invasion” of illegal Mexican immigrants center around two positions: a “push” and a “pull” theory. Treating the migration as a labor migration, a set of hypotheses is tested dealing with economic conditions in the U.S. and Mexico for the 1948–1972 period. The “push” of conditions in Mexico accounts better for the migration than the “pulls” of economic opportunity in the U.S. The out-migration is traced to institutional changes deriving from economic development in Mexico, especially to governmental policies fostering private agricultural development and discouraging peasant agriculture.