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Unlike a permanent injunction, which is an equitable remedy awarded to an injured party, a preliminary injunction is a form of interlocutory relief that is imposed by a court to preserve the status quo during litigation. In patent cases decided since (and often before) the Supreme Court’s 2006 decision in eBay v. MercExchange, courts have applied a four-factor test when considering the issuance of a permanent injunction. A similar test has evolved for preliminary injunctions, following the Court’s decision in Winter v. NRDC. Both the eBay and Winter tests rely heavily on whether the patentee is likely to suffer “irreparable” harm if an injunction is not granted. Yet despite the very different statutory bases and underlying reasoning for preliminary versus permanent injunctions, almost no scholarly attention or judicial reasoning has been devoted to an analysis of the meaning of irreparable harm in the context of preliminary injunctions. In order to gain a better understanding of the information that courts consider when deciding motions for preliminary injunctions, we collected data from 211 published district court opinions in patent cases decided between 2013 and 2020 in which a preliminary injunction was sought. Based on our findings, as well as recent opinions of the Federal Circuit, we find that much uncertainty and lack of clarity surrounding preliminary injunctive relief can be reduced, or eliminated, by explicit recognition that irreparable harm has (or should have) a certain meaning, and that meaning is not the same as harm. We propose a new four-factor test for irreparable harm when assessing the issuance of preliminary injunctions in patent cases. That test provides that to be considered irreparable, harm should be that which, in the absence of an injunction, 1) would unduly disrupt the status quo, 2) is imminent and likely to occur, 3) is causally linked to the alleged infringement, and 4) unlikely to result in payment of adequate compensation. We believe that the application of this new test will make the preliminary injunction analysis more certain and economically sensible, and better fitted to achieve its stated statutory goals.