How is patent infringement determined?

The determination of patent infringement is usually made during the course of a lawsuit involving a claim of infringement. To make this determination, the claims of the patent must be compared to the product which is accused of infringing, because it is the patent’s claims which define the scope of the patent. While patents often contain many claims, a patent is infringed if the product in question infringes even one of the claims. However, a claim is only infringed if every element of that claim is present in the product in question (in legalese, this is known as the claim “reading on” the product). If any element of the claim is missing, the product does not infringe that claim.

While there are several defenses one can raise to argue that their product does not infringe a patent, the most common defense is to attack the patent itself. This is done by arguing that the patent is not valid because, even though it was granted by the PTO, it fails to meet one or more of the requirements necessary for a patent to be granted.