The question of how organized labor affects the content, enforcement, and outcomes of regulation is especially timely in an era in which protective laws and regulations are being scaled back or minimally enforced and union membership is in decline. This article surveys literature from a wide array of regulatory domains—antidiscrimination, environmental protection, product quality, corporate governance, law enforcement, tax compliance, minimum wage and overtime protection, and occupational safety and health—in an effort to identify common findings on what unions do for regulation. Literature on the topic has taken up five questions: how labor unions affect the passage of protective laws and regulations; how they affect the outcomes that regulators target; how they affect the intensity of regulatory enforcement; the specific activities and channels of influence they use to influence regulated outcomes; and the role they play in self-regulation. Drawing on empirical literature from the domains listed, I review and analyze literature on each of these questions and offer several conclusions and suggestions for future research.