Direct infringement occurs when a party unlawfully uses, manufactures, offers to sell, sells, or imports an invention. See 35 U.S. Code § 271. Direct infringement can occur only if a single party practices every limitation of a patent claim.
The fact that an unpatented part of a combination patent may distinguish the invention does not draw to it the privileges of a patent. That may be done only in the manner provided by law. However worthy it may be, however essential to the patent, an unpatented part of a combination patent is no more entitled to monopolistic protection than any other unpatented device.
— Mercoid Corp. v. Minneapolis-Honeywell Regulator Co., 320 US 680, 684 (S. Ct. 1944).
An exception to this rule arises when a single party exercises control or direction over an entire process, so that each limitation of a claim may be attributed to them.
The court started from the proposition that direct infringement requires a single party to perform every step of a claimed method. Id., at 1329. This requirement is satisfied even though the steps are actually undertaken by multiple parties, the court explained, if a single defendant exercises control or direction over the entire process such that every step is attributable to the controlling party.
— Limelight Networks v. Akamai Technologies, 134 S. Ct. 2111, 2116 (S. Ct. 2014).
An infringer may be liable even if the infringer was negligent, had no intention to cause harm, or was unaware of the offense.
Under this form of liability, a defendant's mental state is irrelevant. Direct infringement is a strict-liability offense.
— Commil USA, LLC v. Cisco Systems, Inc., 135 S. Ct. 1920, 1926 (S. Ct. 2015).