Does US policy at the Mexican border—heavily weighted toward immigration and drug law enforcement—help the capitalist system function in North America, and if so, how? And if not, what are the most likely drivers of such policies, and how do they interact with the capitalist context? Four topics are examined: inequalities of rights to border crossing into the United States from Mexico, and the role of such unequal mobility in the maintenance of various privileges in North America; a puzzle in capitalist–functionalist border policy–underinvestment in ports of entry compared to enforcement between such ports; enforcement against unauthorized migrants seen both as labor control and discriminatory politics; and border enforcement and militarization as a system of regional repression and control, addressed at the rapidly growing and important US–Mexico border region. The relationship between US border policies and the functional needs of capitalism is complex, not simple; the article rejects a perfect system view in favor of a richer view of capitalism as filled with contradictory social impulses and political outcomes, shaped in broad contexts of class relations and capital accumulation. The wider context of this essay is the question of how the territorial nation-state relates to capitalism, two fundamental features of our era. Some preliminary thoughts on that question are broached in the conclusion.