54:2 Rethinking Assignor Estoppel


The Supreme Court and the Federal Circuit have repeatedly emphasized the public interest in testing the validity of patents, weeding out patents that should not have been issued. But there is one important group of people the law systematically prevents from challenging bad patents. Curiously, it is the very group patent law is supposed to support: inventors themselves. The century-old doctrine of assignor estoppel precludes inventors who file patent applications from later challenging the validity or enforceability of the patents they receive. The stated rationale for assignor estoppel is that it would be unfair to allow the inventor to benefit from obtaining a patent and later change her tune and attack the patent when it benefits her to do so. The Supreme Court has traditionally disfavored the doctrine, reading it narrowly. But the Federal Circuit has expanded the doctrine in a variety of dimensions, and applied it even when the benefit to the inventor is illusory. Further, the doctrine misunderstands the role of inventor-employees in the modern world.

More important, the expansive modern form of assignor estoppel interferes substantially with employee mobility. Inventors as a class are put under burdens that we apply to no other employee. If they start a company, or even go to work for an existing company in the same field, they will not be able to defend a patent suit from their old employer. The result is a sort of partial noncompete clause, one imposed without even the fiction of agreement and one that binds anyone the inventor comes in contact with after leaving the job. Abundant evidence suggests that noncompetes in general retard innovation and economic growth, and several states prohibit them outright, while all others limit them. But assignor estoppel is a federal law doctrine that overrides those state choices.

It is time to rethink the doctrine of assignor estoppel. I describe the doctrine, its rationale, and how it has expanded dramatically in the past twenty-five years. I argue that the doctrine is out of touch with the realities of both modern inventing and modern patent law, and that it interferes with both the invalidation of bad patents and the goal of employee mobility. Should the Supreme Court take up the doctrine, it is unlikely to survive in its current form. Rather, it should—and will—return to its much more limited roots.