Products liability is the body of state tort law that decides who pays when a product hurts someone, and this UpLaw guide maps the whole system from the collapse of the privity rule to the modern three-category framework. It traces the arc from MacPherson v. Buick through Justice Traynor's Escola concurrence to Greenman v. Yuba Power and Restatement (Second) of Torts § 402A, then to the Restatement (Third) of Torts: Products Liability and its function-specific definitions of manufacturing defect, design defect, and inadequate warning. It explains why plaintiffs plead strict liability, negligence, and warranty together; why the design-defect test genuinely splits the states between consumer expectations and risk-utility with a reasonable-alternative-design requirement; and how the learned-intermediary, sophisticated-user, and bulk-supplier doctrines reroute the duty to warn. It works through the chain of distribution, component-part and successor-liability problems, causation and the heeding presumption, and the full defense arsenal — misuse, substantial alteration, comparative fault, state of the art, regulatory compliance, statutes of repose, and the Boyle government-contractor defense. It closes with federal preemption after Riegel, Wyeth, Mensing, and Bartlett, the economic-loss rule, punitive damages, and the aggregation machinery of Rule 23 and the MDL statute. A running hypothetical — a cordless miter saw made by Vantage Power Tools — carries the doctrine from the accident scene to the verdict form.