Admiralty law (usually referred to as simply admiralty and also referred to as maritime law) is a distinct body of law which governs maritime questions and offenses. Under conventions of international law, the flag flown by a ship generally determines the source of law to be applied in admiralty cases, regardless of which court has personal jurisdiction over the parties.

Sea-borne transport being one of the most ancient channels of commerce, rules for resolution of disputes involving maritime trade developed very early in recorded history. Classical sources of this law include the Rhodian law, of which no primary written specimen has survived, but which is alluded to in other legal texts; Roman and Byzantine legal codes; and the customs of the Hanseatic League.

Admiralty law was introduced into England by Eleanor of Aquitaine while she was acting as regent for her son King Richard the Lionhearted. She had earlier established admiralty law on the island of Oleron (where it was published as the Rolls of Oleron) in her own lands (but she is often referred to in admiralty law books as "Eleanor of Guyenne"), having learned about it in the eastern Mediterranean while on Crusade with her first husband, King Louis VII of France. In England special courts, admiralty courts handle all admiralty cases. These courts do not use the common law of England, but are civil law courts based upon the Corpus Juris Civilis of Justinian.

In the United States, admiralty is under the jurisdiction of the United States district courts and appeal from judgments in admiralty case lies to the United States courts of appeals. However, admiralty courts in the United States are courts of limited jurisdiction, so state courts have concurrent jurisdiction in admiralty when state law claims are at issue. Moreover, state courts may have jurisdiction in admiralty when the matters being adjudicated are local in nature. Under Article III of the United States Constitution, the Supreme Court is the court of last resort for all cases arising under admirality law, although only a few cases on each term's docket will actually deal with admiralty claims.

See: Barratry, Canals, Docks, Navigation, Piers, Piracy, Prize, Sailor, Shipping, Waters, Wharves, Declaration of London, United Nations Convention on the Law of the Sea.