Admiralty is the oldest body of federal law in the United States and still one of the least intuitive: a claim's home is decided not by where the parties live but by where the wrong happened and what it had to do with the sea, and the answer to that question changes the forum, the jury right, the remedy, and often the defendant itself. This guide walks the whole territory — the constitutional grant in Article III and the saving-to-suitors clause of 28 U.S.C. § 1333; admiralty tort jurisdiction under the locality-plus-nexus test of Jerome B. Grubart and contract jurisdiction under the conceptual approach of Norfolk Southern v. Kirby; the distinctive procedure of Rule 9(h), in rem actions, maritime liens and their priority ladder, and arrest and attachment under Supplemental Rules C and B. It then works through maritime personal injury in depth: who counts as a seaman under Chandris, the Jones Act's featherweight causation standard, the shipowner's absolute warranty of seaworthiness, the ancient remedy of maintenance and cure and the punitive damages that Atlantic Sounding restored to it, the Longshore Act's compensation bargain and the § 905(b) vessel-negligence action, and the very different rules that govern passengers and cruise lines. Cargo, charter parties, collision, salvage, general average, limitation of liability, marine insurance after Wilburn Boat, and oil pollution under OPA 90 each get their own treatment, with the leading cases and what they actually held. Throughout, a running hypothetical — an injured deckhand aboard a fictional tug and a fictional cargo loss — shows how the doctrines interlock in a real file. The recurring traps are flagged where practitioners actually fall into them: the missed Rule 9(h) election, the McCorpen concealment defense, the COGSA one-year bar, the six-month limitation deadline, and the state-law surprise lurking inside every marine insurance policy.