Injunctions for Patent Infringement: Historical Equity Practice Between 1790 – 1882


A significant debate in patent law today concerns what remedy a patent owner may receive when a court finds a defendant liable for patent infringement. In eBay v. MercExchange (2006), the Supreme Court held that courts must use a “four-factor test historically employed by courts” for issuing injunctions that represented a “long tradition of equity practice.” Chief Justice John Roberts further claimed in a concurrence that, from “the early 19th century, courts have granted injunctive relief upon a finding of infringement in the vast majority of patent cases.”

Both of these historical claims are conventional wisdom today in law and scholarship, and both claims are empirically unverified. This article tests both historical claims in reporting the results of a database of 899 opinions in which federal courts sat in equity in patent lawsuits. The database comprises opinions by trial courts and appellate courts in lawsuits filed between 1790 and 1880 that are compiled in the Federal Cases reporter.

The database confirms and challenges the conventional wisdom. First, eBay is wrong: there was no four-factor test in the “long tradition of equity practice” in patent cases. In the 899 opinions, no judge applied a four-factor test in granting an injunction, either for a permanent or a preliminary injunction. Second, Chief Justice Roberts is correct: courts did grant permanent injunctions in a vast majority of cases as a remedy for patent infringement. In the 899 opinions, courts awarded permanent injunctions in 93.7% of the cases in which a defendant infringed a valid patent. Given the stark absence of a four-factor test, the article concludes by describing the historical equitable jurisprudence applied by federal courts. Based on the opinions, it describes how courts applied the same equitable doctrines and principles in patent cases as in redressing continuing trespasses of real property, protecting patents as much as they protected real estate and other property interests.