Federal Circuit Report
Skiermont Derby LLP
WILL THE DOCTRINE OF ASSIGNOR ESTOPPEL SURVIVE SCRUTINY FROM THE SUPREME COURT?
The doctrine of assignor estoppel is an equitable, judge-made doctrine that prevents a party who assigned a patent to another from later challenging the validity of the assigned patent. The longstanding reasoning behind the doctrine is that "an assignor should not be permitted to sell something and later to assert that what was sold is worthless, all to the detriment of the assignee."1 "In other words, it is the implicit representation by the assignor that the patent rights that he is assigning (presumably for value) are not worthless that sets the assignor apart from the rest of the world and can deprive him of the ability to challenge later the validity of the patent. To allow the assignor to make that representation at the time of the assignment (to his advantage) and later to repudiate it (again to his advantage) could work an injustice against the assignee."2