In 2005, the Food and Drug Administration required the use of chlorofluorocarbon-free propellants in albuterol inhalers. But 3M held patents on the only U.S.-approved chlorofluorocarbon-free inhaler. The agency’s regulations forced multiple generic albuterol manufacturers to choose between infringing 3M’s patents or exiting the market. This state of affairs was lucrative for 3M, perhaps good for the environment, bad for competition, and terrible for patients faced with high costs for essential medical devices. This is an example of a general phenomenon: mandatory infringement. Intellectual property prohibits certain activities, but sometimes the government also mandates these very same activities. Such situations arise surprisingly frequently in fields including environmental protection, pharmaceutical labeling, information technology, and access to justice. The manifest injustice of regulatory law requiring what intellectual property law disallows has sparked vigorous debates over individual cases in all these fields. Yet there has been no unified treatment of how the law should address mandatory infringement. Courts and scholars have taken approaches that are scattershot, idiosyncratic, and even inconsistent with each other. The key to fixing mandatory infringement is understanding why it is a problem in the first place: competition. Mandatory infringement creates outsized market power due to an inverse relationship between the effect of regulations and intellectual property rights on competition. It further enables passing the buck between regulators and courts, encourages rent seeking rather than innovation, and induces government offloading of licensing costs onto regulated entities that produces a principal–agent disconnect. These phenomena explain why regulators and courts applying antitrust or intellectual property laws have difficulties resolving mandatory infringement. Although they try hard to reach fair outcomes, and often succeed, the distinctive aspects of mandatory infringement and authorities’ ...