Maritime law is a legal body that regulates ships and shipping. As sea-borne transportation is one of the most ancient channels of commerce, rules for maritime and trade disputes developed very early in recorded history. Modern admiralty law, often called simply admiralty or maritime law, has its origins in the classical Rhodian law. No primary written specimen of the Rhodian law has survived, but it is alluded to in Roman and Byzantine legal codes as well as the customs of the Hanseatic League, the dominant trading power of the Middle Ages and Early Modern eras.

While traveling the eastern Mediterranean on the Crusades with her first husband, King Louis VII of France, Eleanor of Aquitaine discovered a complicated and advanced system of admiralty law. She brought back this admiralty law and administered it upon her people on the island of Oleron. Later, while acting as regent for her son King Richard the Lionheart in England she founded the British system of admiralty law. In England, special admiralty courts handle all admiralty cases. The courts do not use the common law of England.

In this same way, admiralty or maritime law is distinct from standard land-based laws even today. Even within another country's claimed waters, admiralty law states that a ship's flag dictates the law. This means that a Canadian ship in American waters would be subject to Canadian law and crimes committed on board that ship would stand trial in Canada. In the United States the Supreme Court is the highest court of appeals for admiralty cases, though they rarely progress beyond the state level. United States, admiralty law is of limited jurisdiction, so it is up to the judges to assign verdicts based on a combination of admiralty and specific state law.

Because admiralty law is such a complicated set of laws, with a rich history and specific cases and implementation, many lawyers focus specifically on the field of admiralty law. If you have a case that falls into this category, your regular personal attorney may not be able to help. The specific circumstances of admiralty jurisdiction make it prudent, and perhaps necessary, that you hire a specific admiralty lawyer.