ABSTRACT
It’s a simple rule: one patent per invention. This is easy to enforce when patent claims in two patents are identical, but what if the second patent claims something close but not quite the same? For more than 150 years, courts have held that obvious improvements over the prior art cannot be patented. But when inventors seek a small improvement in their own follow-on patents, there may not be any prior art because the law does not typically count inventors’ work against themselves. Inventors can include two similar claims in the same patent without objection, but if they split them into two different patents, they might achieve unfair benefits that come along with having two separate patents on the same basic invention. And so the ‘non-statutory’ double patenting bar was born. Each invention must be filed in a single patent, and any other patent applications with ‘patentably indistinct’ material are invalid unless the inventor makes concessions about when the double patent will expire and who may own it – concessions that are not required by the Patent Act. But some argue that even with these concessions, double patenting exacts costs on the patent system, especially with respect to pharmaceutical patent thickets.
But this creates a puzzle. How is it that Congress continues to pass laws that make double patenting easier and more prevalent, while at the same time remaining silent about the potential costs of double patenting? This article reviews the history of double patenting and examines more than thirty years of patenting data to address this and several other puzzles in double patenting. It considers whether the original justification for double patenting makes sense given continuation practice and whether double patenting bars have any continued vitality now that patents all expire based on the earliest priority date. Further, Congress has had an opportunity to limit double patenting but has instead relied on legislative history and rulemaking, both of which are at risk of Supreme Court reversal. This article examines why double patenting bars seem to be on borrowed time yet continue to thrive.
Risch, Michael, The Double Patenting Puzzle (July 8, 2025), Houston Law Review, volume 63, forthcoming 2025.
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