Why has the EPA not regulated fracking? Why has the FDA not regulated e-cigarettes? Why has NHTSA not regulated autonomous vehicles? This Article argues that administrative agencies predictably fail to regulate emerging risks when the political environment for regulation is favorable. The cause is a combination of administrative law and interest group politics. Agencies must satisfy high, initial informational thresholds to regulate, so they postpone rulemaking in the face of uncertainty about the effects of new technologies. But while regulators passively acquire more information, fledgling industries consolidate and become politically entrenched. By the time agencies can justify regulation, the newly entrenched industries have the political capital to thwart them.his Article offers a prophylactic against this predictable regulatory failure. It defends an experimentalist model of regulation, in which agencies are empowered to impose moratoria on risky emerging technologies while regulators organize experiments to learn about the risks they pose and the means to mitigate them. The agency-coordinated experiments would expedite the promulgation of empirically informed rules. The moratoria would extend the political window for regulatory action and protect the public in the interim. The Article applies this experimentalist model to the regulation of fracking, e-cigarettes, and autonomous vehicles. It also identifies legal strategies for implementing experimental regulation under existing law. It challenges the conventional wisdom that agencies should postpone regulation until they can confidently predict the effects of new risky technologies.