How is Mexican immigration changing the United States in the twenty-first century? In the past several decades, the United States has seen an explosion in the number of Hispanic immigrants to this country, most of them from Mexico. And most of them go to California. Today nearly half of all Californians are immigrants or the children of immigrants—most of them coming originally from Mexico. What is the economic and social impact of this influx on California, and what does it bode for the rest of the country? What makes Mexican immigration different than immigration from other countries? And what, if anything, should we do about it?