Reading claims against a product
A patent's claims, the numbered sentences at the end of the document, define what it covers; the drawings and description help interpret them but do not expand them. To infringe a claim literally, an accused product or method generally has to include every limitation recited in it. Where one element is missing, the owner may argue that an equivalent is present, though that doctrine is limited by what the applicant gave up during examination and by earlier technology. Claim charts that map each limitation to evidence about the product are the standard working tool on both sides. How the court construes disputed claim terms, often after a dedicated hearing, frequently shapes the case well before trial.
Direct and indirect theories
Claims are not limited to the company that makes the product, and resellers and customers are sometimes named as well. Induced infringement reaches someone who knowingly encourages another's infringement, and contributory infringement can reach certain suppliers of components. Both indirect theories turn on knowledge of the patent, which is one reason notice letters matter. When customers are sued, their supply agreements may decide who pays for the defense, and suppliers sometimes step in to defend the product directly.
Responses that are usually considered
An accused party commonly looks at non-infringement, invalidity based on earlier technology, and defenses such as a license or exhaustion through an authorized sale. Validity can be challenged in court or, for many patents, through proceedings at the Patent Trial and Appeal Board, which the USPTO has discretion to institute and whose institution practices have shifted recently. Owners, for their part, should check marking, notice, and the strength of the patent against prior art before filing, since a weak patent invites a challenge that can cost more than the case recovers. In a first review we read the asserted claims against the product, identify the limitations that will be disputed, and set out which forum makes sense.
