A patent is a deal between an inventor and the government. The inventor publishes the technical details of an invention; the government grants a 20-year monopoly on making, using, or selling it. After the term expires, anyone can use the technology freely — that is the public benefit. In exchange, for those 20 years, the patent holder can sue anyone who builds the same thing.
That's the theory.
What a patent actually is
A US patent is a document filed with the US Patent and Trademark Office (USPTO) that describes an invention in three pieces:
- The claims — numbered sentences that define the invention's legal scope. Claims are what infringement is judged against. Everything else is context.
- The specification — the technical description, including drawings, examples, and embodiments. This has to be detailed enough that a "person having ordinary skill in the art" could reproduce the invention.
- The abstract — a one-paragraph summary, mostly there for patent searchers.
The claims are the only part that legally matters. A patent with a beautiful 50-page specification but a single narrow claim only protects what that claim says. A patent with a sparse specification but broad claims can cover more than its inventor ever built. (How to read a patent claim →)
Three statutory requirements
Under 35 U.S.C. — the patent statute — a patent must satisfy three substantive tests to be valid:
- Patent-eligible subject matter (§ 101) — the invention must be a process, machine, manufacture, or composition of matter. Abstract ideas, laws of nature, and natural phenomena are off-limits. Alice Corp. v. CLS Bank International (2014) gave courts a two-step test for sorting abstract ideas from patentable processes.
- Novelty (§ 102) — the invention must be new. If anyone, anywhere in the world, publicly disclosed the same thing before the inventor's filing date, the patent isn't novel. (Prior art and § 102 →)
- Non-obviousness (§ 103) — the invention must be more than a trivial combination of things already known. KSR v. Teleflex (2007) is the modern touchstone for how courts decide what counts as obvious. (Obviousness under § 103 →)
A patent that fails any of these is invalid. The catch: most invalidity defenses don't get tested unless someone is willing to spend enough money to challenge the patent. (For a worked example covering all six dossier sections — summary, litigation, § 102, § 103, extensions, and derivative works — see US Patent 8,069,073, the Lumen View patent we use as the running example throughout this site.)
What a patent doesn't give you
Common misconceptions:
- A patent is not the right to make your invention. It's the right to exclude others. If your patent reads on someone else's earlier patent, you may be the one infringing.
- A patent doesn't mean the USPTO checked everything. Examiners have a limited number of hours to evaluate each application and search prior art with the tools available to them. They routinely miss references that would invalidate the patent.
- A patent doesn't get stronger over time. It expires 20 years after the earliest non-provisional filing date, sooner if maintenance fees aren't paid.
Why bad patents matter
The economics of patent litigation make weak patents a profitable weapon. A complaint costs about $400 to file in federal court. Defending one through trial averages several million dollars and routinely exceeds that for complex cases. The AIPLA Economic Survey is the standard reference for these numbers. Most defendants settle for less than the cost of fighting — even when the patent wouldn't survive serious scrutiny.
The PTAB (Patent Trial and Appeal Board) confirms what defendants suspect: when bad patents are seriously challenged through Inter Partes Review, most institute and most lose at least one claim. The trolls' leverage isn't their patents — it's the cost of proving the patents are bad. (Patent reviews: IPR, PGR, reexam →)
Bottom line
A patent is a powerful but fallible legal instrument. Most patents that get litigated would not survive if they were seriously challenged. Knowing what a patent actually says — and what it has to say to be valid — is the first step in defending against one. Browse our patent database for tracked patents with full dossiers, or add a patent we haven't analyzed yet.
This article is for general education and is not legal advice.