A complete practitioner's treatment of American defamation law, built for both sides of the case. Part I sets out the prima facie case element by element, including the defamatory-meaning inquiry, the of-and-concerning requirement, publication and republication, and the surviving libel-slander distinction. Part II builds the constitutional overlay from New York Times Co. v. Sullivan through Gertz, Dun and Bradstreet, and Hepps, explaining how plaintiff status and subject matter jointly determine the fault standard, the burden of proving falsity, and the availability of presumed and punitive damages. Part III works the fact-opinion line after Milkovich and the defamation-by-implication theory. Part IV catalogs the absolute and qualified privileges, including the fair report privilege and its limits. Part V covers the adjacent torts that plaintiffs plead alongside or instead of defamation. Part VI addresses the internet layer: Section 230, unmasking anonymous speakers, the single publication rule, and generative AI. Part VII is procedure from pre-suit demand through anti-SLAPP, pleading, discovery, summary judgment, and appeal. Part VIII covers damages, injunctions and the prior restraint doctrine, retraction statutes, and insurance. Part IX is publisher-side risk management, and Part X is the state-variation map that has to be verified in every case.