Anyone who assigns patent rights to another in exchange for valuable consideration implicitly acknowledges the validity of the patent and therefore gives up the right to challenge the validity of that patent at a later time. This principle, known as assignor estoppel, is rooted in principles of fairness: "[a]n assignor should not be permitted to sell something and later assert what was sold was worthless, all to the detriment of the assignee." Diamond Scientific Co. v. Ambico, Inc., 848 F.2d 1220, 1225 (Fed. Cir. 1988).
This policy has questionable underpinnings, because for all of the focus on the fairness between the assignor and the assignee, what is largely forgotten is that patent rights also involve the public at large. For if sound reasons really exist for invalidating a patent, and the assignor is estopped from bringing them to the court's attention, isn't this a gross disservice to the public at large? After all, a monopoly was granted when it shouldn't have been, and instead of correcting that, we just let the monopoly stand as a matter of fairness to the assignee,
Luckily, assignor estoppel can be circumvented -- just have some party other than the assignor bring the invalidity challenges, and then all issues of fairness quickly evaporate.
This policy has questionable underpinnings, because for all of the focus on the fairness between the assignor and the assignee, what is largely forgotten is that patent rights also involve the public at large. For if sound reasons really exist for invalidating a patent, and the assignor is estopped from bringing them to the court's attention, isn't this a gross disservice to the public at large? After all, a monopoly was granted when it shouldn't have been, and instead of correcting that, we just let the monopoly stand as a matter of fairness to the assignee,
Luckily, assignor estoppel can be circumvented -- just have some party other than the assignor bring the invalidity challenges, and then all issues of fairness quickly evaporate.
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