Assignor estoppel is the doctrine that prevents an inventor from challenging the validity of a patent after he assigns the patent rights to someone else. Unlike licensee estoppel, assignor estoppel is generally supported by patent law.

Why Would I Want to Challenge the Validity of the Patent on My Invention?

If you assign your rights to a patent, but then later decide that you would like to manufacture and sell the invention yourself, you cannot do so without infringing on the patent rights if the patent is valid.

Why Is It So Bad to Challenge the Validity of My Patent?

One of the biggest problems with challenging the validity of a patent after you assign it to someone is that you probably made some kind of financial gain off of the assignment. Patent law wants to prevent you from selling rights to your patent and then, once you¿ve made a profit, turning around and declaring those rights worthless. If not for assignor estoppel, an inventor could sell his patent rights, get the patent declared invalid, and then go right back and manufacture and sell the invention whose patent rights he sold.

Are There any Exceptions to Assignor Estoppel?

Assignor estoppel is a pretty rigidly applied doctrine. However, under certain circumstances, courts will not bar an assignor from challenging the validity of the patent on his own invention. The most common of these exceptions occurs when the invention was disclosed in a prior patent. If an earlier patent disclosed the invention, the need to avoid extending the duration of patent protection outweighs the need to prevent assignors from abusing their patents.

How Can I Avoid Having to Deal with Assignor Estoppel?

The best way to avoid dealing with assignor estoppel is to be careful when making assignments because most of the time, if you make an assignment, it will be hard to get your patent rights back.

  • Make sure you are getting adequate compensation for your invention when you make the assignment
  • Limit the duration of the assignment if possible

Do I Need a Patent Attorney?

If you are an assignor or an assignee of patent rights and have questions or concerns regarding your rights, you may want to consult with a patent lawyer. An experienced patent attorney will let you know how assignor estoppel may affect you and, if necessary, a patent attorney can represent you in court.