Please ensure Javascript is enabled for purposes of website accessibility

Federal Circuit discusses written description requirement, assignor estoppelSeptember 20, 2005

In Pandrol USA, LP v. Airboss Railway Products, Inc., decided on Monday, Sept. 19, the Federal Circuit Court of Appeals restated the requirement for an adequate written description of a patent and addressed the issue of assignor estoppel. The patent at issue dealt with a railroad track fastening system designed to reduce erosion of the concrete rail tie to which it is fastened.Under Section 112 of the patent statutes, patent applications must contain a written description of the invention. The purpose of this requirement is to ‘prevent an applicant from later asserting that he invented that which he did not; the applicant for a patent is therefore required to recount his invention in such detail that his future claims can be determined to be encompassed within his original creation.’ This is closely related to the concept of ‘new matter,’ the doctrine that prevents a patent applicant from adding new information or ideas after the application is originally filed. In Pandrol, the Court reaffirmed its precedent in written description cases, stating that an adequate written description ‘requires sufficient information in the specification to show that the inventor possessed the invention at the time of the original disclosure.’ This requirement, along with the prohibition on adding new matter, illustrates the importance of having as much information as possible in the first filed patent application, whether that first filed application is provisional or regular.In addition, the Court applied the doctrine of assignor estoppel to prevent the inventor of the patent from testifying that the patent was invalid. Assignor estoppel prevents a party who has assigned the rights to a patent (or application) ‘from asserting that its own patent, for which it may have received value upon assignment, is invalid and worthless.’ The Court noted there are four justifications typically given for assignor estoppel: to prevent unfairness and injustice, to prevent the assignor from benefiting from his own wrong, adopting by analogy estoppel by deed in real estate, and adopting by analogy the landlord-tenant relationship. Here, the Court noted that prevention of unfairness and injustice was the applicable rationale, and affirmed the district court’s decision not to allow the inventor of the patent to testify in support of the defendant’s invalidity defense. The concept of assignor estoppel is important to remember, particularly in cases where an inventor assigned his or her patent to a prior employer and later goes to work for a competitor accused of infringement of that patent. In such a situation, the inventor will not be permitted to testify that the patent is invalid on behalf of his or her new employer. This also would apply if one company assigns a patent to another company, except that in that case, the assigning company would, most likely, not be able to assert invalidity as a defense at all.For the complete court decision, visit

← Return to News & Events

Stay in Touch

Receive the latest news and updates from us and our attorneys.

Sign Up