A utility patent protects how an invention works—its function, structure, or method—and is the instrument most people mean when they say "patent." This UpLaw primer walks the whole arc: the four statutory categories of eligible subject matter under 35 U.S.C. § 101, the judicial exceptions policed by the Alice/Mayo framework, and the four substantive requirements of utility, novelty (§ 102), non-obviousness (§ 103), and disclosure (§ 112, after Amgen v. Sanofi). It dissects the anatomy of an issued patent and explains why the claims, not the prose, carry the value. It compares provisional and nonprovisional filings, traces prosecution from first Office Action to Notice of Allowance, and maps the 20-year term, maintenance-fee schedule, and real costs. A running hypothetical—an EMT's self-locking tourniquet—keeps the doctrine concrete, and the piece closes by weighing utility patents against design patents, plant patents, and trade secrets.