What trips people up most is that copying is not required. Someone can infringe a patent by making, using, selling, offering to sell, or importing a covered invention without permission, even if they came up with it on their own. Patent infringement is the unauthorized use of an invention protected by a U.S. patent. The basic rule comes from 35 U.S.C. § 271. The patent's claims matter most because they define exactly what is legally protected.

In practice, infringement turns on a side-by-side comparison between the patent claims and the accused product, process, or technology. If all required parts of a claim are present, infringement may exist. A patent owner can sue for damages, seek an injunction, and in some cases recover enhanced damages for willful infringement under 35 U.S.C. § 284. Patent disputes are usually filed in federal court because patents are governed by federal law, and the U.S. Patent and Trademark Office administers patents under laws passed by Congress and agency rules found in the Code of Federal Regulations.

For a business or inventor, an infringement claim can stop sales, tie up money, and force expensive redesigns. It can also become a valuable asset claim if someone else is using protected technology without permission. Timing, claim wording, prior art, and licensing rights often decide whether a case is strong or weak.