The patent owner is granted the right to exclude others from making, using, selling, offering to sell, and importing the claimed invention. When others violate certain exclusive rights granted to the patentee, the patentee can bring a claim for patent infringement against those that have done one of the activities mentioned above without obtaining the permission of the patentee. In other words, where the alleged infringer violated one of those exclusive rights and cannot show that the patentee granted a license or made an assignment of the patent to them, they may be found liable for patent infringement.

Unlike applications to obtain patents, patent infringement actions are brought directly to federal district court. There are two ways that patent infringement can be shown; by a showing of literal infringement and by a showing under the doctrine of equivalents. Literal infringement exists where each and every aspect of each patent claim corresponds identically to an aspect of the allegedly infringing device or process. Alternatively, infringement exists under the doctrine of equivalents where an element of the allegedly infringing device or process performs substantially the same function, in substantially the same way, to achieve substantially the same result. If any aspect of this three-part test under the doctrine of equivalents is not satisfied, the infringement inquiry ends and there can be no liability. That said, there are certain limitations on the doctrine of equivalents. For example, if during the prosecution history of a particular patent a particular subject matter was dropped from the coverage of the patent in order for the patent to be granted, the patentee cannot later claim coverage of that subject matter by way of the doctrine of equivalents. This is known as prosecution history estoppel. Prior art also limits the scope of the doctrine of equivalents, given that the equivalents under the doctrine may not include any invention that constitutes prior art.

Patent infringement liability also extends to those that induce infringement, or who are responsible for contributory infringement. These cases of infringement are indirect rather than direct, and can arise where an otherwise innocent party becomes involved with an infringing party in any one of a number of ways. The patent act states that “whoever sells a component of a patented machine, manufacture, combination or composition, or a material or apparatus for use in practicing a patented process, constituting a material part of the invention, knowing the same to be especially made or especially adapted for use in an infringement of such patent, and not a staple article or commodity of commerce suitable for substantial non-infringing use, shall be liable as a contributory infringer.”

Regardless of the theory under which the owner of a patent chooses to sue the alleged infringer, the remedies are the same, and they are substantial. The applicable patent laws state that a person or entity found liable for patent infringement may be subject to damages equivalent to the patentee’s lost profits, but not less than a reasonable royalty, as well as an injunction. In cases where the infringement is willful, the court can award treble damages and attorneys’ fees.