When filing a patent application, one must include a list of all inventors. Determining inventorship can be difficult, and getting it wrong can render an issued patent invalid. There is some good news, however. In the majority of cases, inventorship errors can be corrected, provided the correction is made before the patent is invalidated at trial.

Errors of inventorship can arise when one of the following occurs:

1. An individual is incorrectly named among the listed co-inventors (referred to as "misjoinder")
2. An actual inventor is not named among the co-inventors (referred to as "nonjoinder")
3. A combination of the above occurs
4. An inventor is fraudulently named (e.g., a president or CEO insists on being named as an inventor for all company patents)

The misjoinder of a person who did not contribute to some aspect of one or more of the claims of the patent could theoretically render the patent invalid. However, courts have opened the door to some flexibility, noting that the misjoinder of an inventor should not invalidate a patent and the mistake should be corrected quickly. For example, in Stark v. Advanced Magnetics, Inc., the Federal Circuit stated in 1997 that the correction of a misjoinder—whether deceptive and dishonest or merely uninformed and honest—would be allowed to preserve the validity of the patent.

Nonjoinder issues, on the other hand, do not fall under the Federal Circuit's lax misjoinder position and can cause serious problems during patent enforcement. The nonjoinder of an inventor can invalidate a patent entirely. It can also provide the excluded inventor with full, undivided equal rights to the patent, which he or she can then assign to a different party (e.g., a competitor or the entity charged with infringement). Under U.S. patent law, in the absence of an agreement to the contrary, each joint owner may exploit the invention without the permission of, and without accounting to, the other joint owner(s). Thus, one joint owner cannot stop another from independently selling, conveying, assigning or licensing the subject matter of the patent.

The leading case on the issue of nonjoinder is Ethicon, Inc. v. U.S. Surgical Corporation, decided by the Federal Circuit in 2001. In the Ethicon case, U.S. Surgical was sued by Ethicon for patent infringement. As a defense, U.S. Surgical filed a motion with an unnamed inventor seeking to invalidate the patent. The Federal Circuit eventually held that the unnamed inventor must be added to the patent. Since he was not required to assign rights to Ethicon, the unnamed inventor granted U.S. Surgical a license to his rights. Consequently, Ethicon's infringement action against U.S. Surgical was dismissed because of the license from the unnamed inventor. The Ethicon case illustrates the importance of obtaining assignments or agreements from all individuals who work on projects, especially if the individuals are independent contractors or non-employees who may not have a strict duty to assign their rights to the company.

Therefore, when determining who qualifies as an inventor, it is important to identify who contributed to the conception of the idea as claimed, and who was involved in reducing the idea to practice. You should also remove from the patent application any individuals who were working under the direction of another and, therefore, did not contribute original thought to the claimed invention. Given the complexities of these issues and the problems companies could face if there are errors of inventorship, it is important to consult with a patent attorney who can help you navigate these choppy waters.