United States antitrust law rests on three statutes and a century of judicial gloss, and this UpLaw guide maps the whole system from the agreement requirement of Sherman Act Section 1 to the exclusionary-conduct inquiry of Section 2, the merger standard of Clayton Act Section 7, and the broader unfair-methods jurisdiction of FTC Act Section 5. It explains why the law protects competition rather than competitors, how courts sort restraints into per se offenses and rule-of-reason cases, and how the burden-shifting framework confirmed in Ohio v. American Express and NCAA v. Alston actually runs in practice. It traces the leading cases — Copperweld, Twombly, Socony-Vacuum, Leegin, Sylvania, Grinnell, Trinko, Aspen Skiing, Brooke Group, Brunswick, and Illinois Brick — and says what each one really held rather than what it is popularly thought to hold. It works through monopoly power and market definition, refusals to deal, tying and bundling, predatory pricing, exclusive dealing, and the structural presumption in merger review, then turns to antitrust injury, standing, the indirect-purchaser bar and its state repealers, the four-year limitations period, treble damages, criminal exposure, and the DOJ leniency program. Two running hypotheticals — a trade association that circulates member pricing data and a dominant ordering platform — carry the doctrine from theory into the conference room. Cross-references route you to UpLaw's deeper treatments of merger review, HSR clearance, compliance programs, class actions, and government investigations.