The adoption of prior user right in U.S. patent law was a big deal, largely aligning the U.S. with the rule in other countries. Simultaneous or near-simultaneous invention is extremely common, so prior use should be as well.

But a surprising thing has happened in the last thirteen years: virtually nothing. Only three decisions in those thirteen years involve substantive claims of prior use. All are by district courts, and two of those decisions were made on largely procedural grounds. Only a single case actually finds prior use by another under the statute.

I document the surprising absence of prior user right litigation. I consider a number of reasons for the missing caselaw, none entirely satisfactory. I consider and (mostly) reject explanations that are a function of when and how cases are litigated, the difficulty of detecting non-public uses, and the existence of prior art as an alternative to the defense. Nor does the explanation seem to be that simultaneous use without publication is no longer as important as it once was. Instead, the real reason no one uses the prior user right is likely a function of the significant limits Congress put on the exercise of the right. It may be time to revisit those limits.