Infringement of a patent is the unauthorized making, using, importing, offering for sale or selling any patented invention within the United States. An individual may be an infringer if he “actively induces infringement of a patent.” Also, an individual who sells a product knowing it is especially made or adapted for use in an infringement of a patent shall be liable as a “contributory infringer.”

As stated previously, the claims of a patent define the scope of coverage against infringers. The broadest valid claim is utilized to determine infringement of the patent. The accused infringing product must literally “read” on every element of the broadest valid claim in the patent.

When litigating a utility patent, the meaning of the claims are determined by the trial judge. When the meaning of a claim is contested, many courts will hold a “Markman hearing” to resolve as a matter of law, the meaning of the claims which defines the scope of the patent . This sometimes requires expert testimony, either technical, patent or both.

Where only insignificant differences exist between the elements of a claim and the infringing product, the Doctrine of Equivalents may be utilized to find infringement. The purpose of the doctrine is to catch unscrupulous copiers who make unimportant and insubstantial changes and substitutions which, though adding nothing, avoid the literal language of the claims.

Finding infringement on a design patent requires determining if an ordinary observer would be deceived by two substantially similar designs.


Although patents are granted by the federal government, the burden of enforcing the patent right is on the patent owner. The primary remedy for patent infringement is a civil action brought in federal court by the patent owner. If a party to an infringement action desires to appeal the decision of the district court, he must appeal to the Court of Appeals for the Federal Circuit (CAFC).

Co-ownership of patents poses a potential problem for enforcing patent rights against infringers. Absent an agreement to allow suit unilaterally, no single co-owner may sue a third party for infringement without the other co-owners’ voluntarily joining the suit.

The general rule regarding assigned patents is that the assignor has no right to enforce the patent against infringers. An assignee may bring an infringement action against an infringer without the assignor joined as a party.

Absent an express covenant requiring enforcement of licensed patent rights, there is no obligation on the part of a licensor to protect the licensee against competition from infringers. An exclusive licensee generally has standing to bring suit for infringement of the licensed patent without joining the licensor as a plaintiff. However, a nonexclusive licensee needs an explicit provision in the license allowing the licensee to enforce a licensed patent, and the licensor must be joined as a plaintiff.


For an owner of a patent to receive damages in any action for infringement, there must be proof that the infringer had “notice” of the patent. Notice can be achieved by either (i) marking the product, (ii) sending a cease and desist letter to the infringer, or (iii) filing an action for infringement. The infringer’s knowledge of the patent and/or infringement is irrelevant. Specific and actual notice to the accused infringer charging infringement of the patent is usually required.  However, if no product is made by the patent owner or licensee, or if a patent has only method claims, neither marking nor actual notice are required.

Marking the product “Patent” or “Pat.” together with the number of the patent is the best form of notice available such as: Patent No. 5,432,594. It provides notice to the public that the product is patented. By marking the product, the owner of the patent is able to receive damages from an infringer back to the date the notice was placed on the product, limited to six years.

Without the notice placed on the product or packaging, the owner of the patent can only receive damages if (i) he notifies the infringer of the infringement, and (ii) the infringer continues to infringe after the notice. Notice may be achieved by sending a cease and desist letter or by filing a civil lawsuit in Federal court for infringement.

It should be noted that sending a cease and desist letter to an infringer may be a mistake for jurisdictional reasons. If a cease and desist letter is sent to an accused infringer, the accused infringer may bring a declaratory judgment against the owner of the patent in an unfavorable jurisdiction to the patent owner. Therefore, prior to sending a cease and desist letter to an accused infringer, the patent owner should consider filing an infringement action in a favorable jurisdiction to avoid being unexpectedly brought into an unfavorable jurisdiction.


The patent owner may seek injunctive relief against the infringing party. The court has the discretion to prevent violation of the rights secured by the patent “on terms as the court deems reasonable.”

Regardless of the circuit in which the case is filed, the two principal considerations involved in determining whether a preliminary injunction should issue are: (1) likelihood of success on the merits, and (2) irreparable harm. To be successful in a patent case, on the merits, the patent must be valid and infringed. The Court of Appeals for the Federal Circuit has stated that irreparable injury must be presumed where validity and continued infringement are clear.


The patent owner may also seek monetary damages to compensate him for the infringement. The award should never be less than a “reasonable royalty” together with interest and costs as fixed by the court. Damages which may be recovered in patent infringement litigation has evolved into two general types:
(i) the patentee’s lost profits, or (ii) royalty-based damages.

If the patent owner is able to prove with reasonable probability his lost profits, then that amount is usually the measure of damages for the patent owner. If lost profits cannot be ascertained, then a reasonable royalty is the measure of the patent owner’s damages.

Punitive damages are also available. The court may make an award of up to three times the amount of actual damages when the infringement is determined to be willful.


An accused infringer has various defenses to a charge of infringement. The most common defense is that there is no infringement – in other words the accused product does not “read” on all of the elements of the broadest claim.

The accused infringer may also attack the validity of the patent. He may use prior art which was not considered by the patent examiner to prove that the patented invention was either not new or was obvious to one skilled in the art when the patent was filed. However, every patent is presumed valid and the burden is on the party seeking to prove invalidity. The accused infringer must prove by clear and convincing evidence that the patent is invalid. The accused infringer must prove the invalidity of every claim that his product would otherwise infringe since the validity of a dependent claim is not affected by the validity of any previous claims.