Mare Liberum

work by Grotius

Also known as: “The Freedom of the Seas”

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June 26, 2026

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Mare Liberum, or "The Freedom of the Seas," is a seminal work by Hugo Grotius published in 1609. It argued that the oceans are international waters and cannot be claimed by any single nation, a principle that became a cornerstone of international law.12

Grotius's argument arose from a dispute where Spain and Portugal claimed exclusive trading rights in the East Indies. The Dutch East India Company commissioned Grotius to defend their right to trade freely. While his larger work, De Jure Praedae, remained unpublished, the chapter on the freedom of the seas, Mare Liberum, was widely circulated and supported the Dutch position in negotiations with Spain. This doctrine, advocating for the open access of the high seas to all nations, eventually gained acceptance in the 19th century and now includes freedoms of navigation, fishing, and overflight.132

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Western philosophy
Political philosophy
…and the resulting two treatises, The Freedom of the Seas (1609) and On the Law of War and Peace (1625), were the first significant codifications of international law. Their philosophical originality lay, however, in the fact that, in defending the rights of a small, militarily weak nation against the powerful…
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…and the resulting two treatises, The Freedom of the Seas (1609) and On the Law of War and Peace (1625), were the first significant codifications of international law. Their philosophical originality lay, however, in the fact that, in defending the rights of a small, militarily weak nation against the powerful…
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Hugo Grotius
Involvement in politics
…appeared under the famous title Mare Liberum (The Freedom of the Seas) in 1609. The work buttressed the Dutch position in the negotiations with Spain regarding the Twelve Years’ Truce and was widely circulated and often reprinted.
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…appeared under the famous title Mare Liberum (The Freedom of the Seas) in 1609. The work buttressed the Dutch position in the negotiations with Spain regarding the Twelve Years’ Truce and was widely circulated and often reprinted.
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John Selden
…in rebuttal to Hugo Grotius’ Mare liberum (1609). From 1640, having reversed his political position once more, he took part in the Commons’ proceedings against William Laud, archbishop of Canterbury, and against Charles I himself.
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…in rebuttal to Hugo Grotius’ Mare liberum (1609). From 1640, having reversed his political position once more, he took part in the Commons’ proceedings against William Laud, archbishop of Canterbury, and against Charles I himself.
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