Immigration reforms in the United States initiated in the 1960s are widely thought to have opened the door to mass immigration from Asia and Latin America by eliminating past discriminatory policies. While this may be true for Asians, it is not the case for Latin Americans, who faced more restrictions to legal migration after 1965 than before. The boom in Latin American migration occurred in spite of rather than because of changes in US immigration law. In this article we describe how restrictions placed on the legal entry of Latin Americans, and especially Mexicans, set off a chain of events that in the ensuing decades had the paradoxical effect of producing more rather than fewer Latino immigrants. We offer an explanation for how and why Latinos in the United States, in just 40 years, increased from 9.6 million people and 5 percent of the population to 51 million people and 16 percent of the population, and why so many are now present without authorization.