Ordinarily, a plaintiff filing a lawsuit bears the burden of proving its case. A defendant can often use the plaintiff’s burden to its advantage by showing that the plaintiff lacks evidence on a crucial point of proof or that the evidence as a whole is insufficient to prove the plaintiff’s case. That rule generally applied in patent cases as well. However, there was some question as to who should bear the burden of proof of infringement in a declaratory judgment action involving a patent. The answer to the question of who bears the burden of proof in a case can have a tremendous impact on strategy and discovery costs.

In Medtronic, Inc. v. Mirowski Family Ventures, LLC, a patent license from Mirowski required Medtronic to pay royalties on licensed products. If a product would infringe but for the license, a royalty on that product was due. Mirowski claimed that Medtronic owed additional royalties for products. Medtronic filed suit, asking the court to declare that because the products identified by Mirowski did not infringe, Medtronic did not owe royalties. Because Medtronic did not breach the license, Mirowski could not bring a counterclaim for patent infringement.

The appeals court had determined that as plaintiff, Medtronic had the burden of proving its products did not infringe. The Supreme Court, in a unanimous opinion, reversed the lower court and held that a patent holder always must prove infringement, even when defending a declaratory judgment action. Licensees can potentially use this decision to their advantage by requiring patent holders to prove infringement before paying royalties. Patent holders will need to ensure their claims of infringement are supported by adequate proof to collect royalties they may have thought were secure.