Mare Liberum in the context of Law of the Sea

Hugo Grotius (/ˈɡroʊʃiəs/ GROH-shee-əss; 10 April 1583 – 28 August 1645), also known as Hugo de Groot (Dutch: [ˈɦyɣoː də ˈɣroːt]) or Huig de Groot (Dutch: [ˈɦœyɣ də ˈɣroːt]), was a Dutch humanist, diplomat, lawyer, theologian, jurist, statesman, poet and playwright. A teenage prodigy, he was born in Delft and studied at Leiden University. He was imprisoned in Loevestein Castle for his involvement in the controversies over religious policy of the Dutch Republic, but escaped hidden in a chest of books that was regularly brought to him and was transported to Gorinchem. Grotius wrote most of his major works in exile in France.

Grotius was a major figure in the fields of philosophy, political theory and law during the 16th and 17th centuries. Along with the earlier works of Francisco de Vitoria and Alberico Gentili, his writings laid the foundations for international law. Two of his books have had a lasting impact in the field: De jure belli ac pacis (On the Law of War and Peace) dedicated to Louis XIII of France and the Mare Liberum (The Free Seas) for which Grotius has been called the "father of international law." Grotius has also contributed significantly to the evolution of the notion of rights. Before him, rights were, above all, perceived as attached to objects; after him, they are seen as belonging to persons, as the expression of an ability to act, or as a means of realizing something.

Law of the sea (or ocean law) is a body of international law governing the rights and duties of states in maritime environments. It concerns matters such as navigational rights, sea mineral claims, and coastal waters jurisdiction. The connotation of ocean law is somewhat broader, but the law of the sea (anchored in the United Nations Convention on the Law of the Sea (UNCLOS)) is so comprehensive that it covers all areas of ocean law as well (e.g., marine environmental law, maritime law).

While drawn from a number of international customs, treaties, and agreements, modern law of the sea derives largely from the United Nations Convention on the Law of the Sea. That convention is effective since 1994, and is generally accepted as a codification of customary international law of the sea, and is sometimes regarded as the "constitution of the oceans".