Created: 04 March 2025
The United Nations Convention on the Law of the Sea (UNCLOS) is the central international framework governing activities at sea. It organizes maritime space, allocates coastal and global rights, and sets the duties that keep navigation, resource use, and maritime security within a rules-based order. UNCLOS is best understood as a distribution of authority, as it defines who may do what, where, and under what limitations.[1]
At its core, UNCLOS balances competing interests. It strengthens coastal State control close to shore, preserves essential freedoms farther out, and conditions both on responsibility, restraint, and due regard for the rights of others.[2]
Baselines: The Legal Starting Point
All maritime zones under UNCLOS are measured from baselines, the legal starting point from which distances such as 12 nautical miles and 200 nautical miles are calculated.[3] Baselines matter because they determine where the coastal authority begins and how far it extends seaward. A sound understanding of baselines is, therefore, foundational: the legality of a maritime entitlement often depends on the legality of the line from which it is measured.
Sovereignty and Jurisdiction: Authority as Distance Increases
UNCLOS draws a sharp line between sovereignty, sovereign rights, and jurisdiction. Sovereignty applies in internal waters (landward of the baseline) and the territorial sea (up to 12 nautical miles),[4] while more limited sovereign rights and jurisdiction apply beyond, particularly in the EEZ and continental shelf.
In the territorial sea, foreign ships enjoy innocent passage so long as passage is not prejudicial to the peace, good order, or security of the coastal State; UNCLOS also identifies activities that make passage non-innocent.[5]
Further, a coastal State may enforce limited controls in the zone contiguous to its territorial sea area extending up to 24 nautical miles from its coast. In this zone, the State may act to stop or penalize violations of its customs, fiscal, immigration, or sanitary laws and regulations affecting its land territory or territorial waters.[6]
Navigation Regimes: The Operational Backbone
UNCLOS protects maritime movement through distinct passage regimes, each with its own legal conditions:
- Innocent passage is a ship-only regime in the territorial sea and, by specific rule, through archipelagic waters. It is conditioned on “innocence,” and the coastal/archipelagic State may take necessary steps to prevent passage that is not innocent. [7]
- Transit passage applies through straits used for international navigation between one part of the high seas or an EEZ and another. It is designed to ensure continuous and expeditious passage for ships and aircraft through essential chokepoints and is not subject to suspension. [8]
- For archipelagic States, UNCLOS also recognizes archipelagic sea lane passage (ASLP), a stronger, transit-type corridor regime for ships and aircraft through and over archipelagic sea lanes and air routes. Sea lanes may be designated, but if they are not, ASLP may still be exercised through routes normally used for international navigation; unlike innocent passage, ASLP is not framed around an “innocence” test and is not subject to suspension.[9]
Taken together, these regimes are the operational engine of UNCLOS: they turn “freedom of navigation” into predictable legal pathways rather than contested political claims.
Jurisdiction at Sea: Flag State, Coastal State, and Port State
Maritime law is enforceable because authority at sea is structured through three main jurisdictional anchors:
- Flag State jurisdiction. As a general rule, vessels on the high seas are subject to the jurisdiction of their flag State, which carries primary responsibility for regulation, safety, and compliance.[10]
- Coastal State jurisdiction. Coastal State powers increase as waters approach the coast, and in specific zones, UNCLOS confers targeted regulatory authority.
- Port State control. When vessels enter port, port States have significant leverage to enforce international and domestic standards, particularly on safety, labor, and pollution control.[11]
This jurisdictional structure is not theoretical; it is how the law of the sea operates in practice, especially in enforcement and compliance.
The Exclusive Economic Zone (EEZ): Sovereign Rights
The EEZ may extend up to 200 nautical miles from the baseline. In the EEZ, the coastal State has sovereign rights for exploring, exploiting, conserving, and managing natural resources (living and non-living), and jurisdiction over specified matters such as installations, marine scientific research, and environmental protection.[12]
Other States retain freedoms of navigation and overflight and other internationally lawful uses associated with those freedoms. The balance is maintained through due regard: both coastal States and user States must exercise their rights with due regard for the rights and duties of others under UNCLOS.[13]
The Continental Shelf: Seabed Rights and Inherent Entitlement
Separate from the EEZ, the coastal State exercises sovereign rights over the continental shelf for exploring and exploiting its natural resources. These rights are over the seabed and subsoil and do not affect the legal status of the superjacent waters or the airspace above. Continental shelf rights are inherent; they exist by operation of law and do not depend on occupation or express proclamation.[14]
The High Seas: Freedoms, Responsibility, and Jurisdiction
Beyond national jurisdiction lie the High Seas: no State may claim sovereignty over any part of them, and all States enjoy core freedoms, including navigation and overflight, the laying of submarine cables and pipelines, fishing, and scientific research. [15] The high seas are reserved for peaceful purposes, and States must exercise their freedoms with due regard for the interests of other States and for activities in the Area.
As a general rule, on the high seas, ships are normally governed by the laws of the country whose flag they fly. Other States generally cannot interfere, except in a few special cases under international law. A State may, however, enforce certain rules once a vessel voluntarily enters its port.[16]
The Area: The Common Heritage of Mankind
The seabed beyond national jurisdiction, “the Area” and its resources are designated as the common heritage of mankind. No State may claim or exercise sovereignty or sovereign rights over any part of it. Activities are regulated through an international regime administered by the International Seabed Authority.[17]
Protection of the Marine Environment: A Legal Duty
UNCLOS treats marine environmental protection as a binding obligation. States must prevent, reduce, and control pollution; protect and preserve marine ecosystems; and cooperate regionally and globally.[18] Environmental compliance is therefore not merely policy; it is part of the legal discipline of maritime governance, shaping both civil and security operations at sea.
Peaceful Settlement of Disputes:
UNCLOS provides a structured framework for resolving maritime disputes through peaceful means. These include negotiation, mediation, conciliation, and, where applicable, binding settlement before the International Tribunal for the Law of the Sea, the International Court of Justice, or arbitral tribunals.[19] While there are jurisdictional limits and recognized exceptions in the UNCLOS system, its central purpose remains clear: to channel maritime disputes into legal processes and reduce the risk of escalation.
Conclusion
UNCLOS endures because it organizes the oceans through a clear distribution of authority, defining who may act, where, and within what limits. By balancing coastal State control with shared maritime freedoms, and conditioning both on responsibility and due regard, it disciplines maritime competition and limits the risk of conflict. UNCLOS is not abstract law; it is the practical framework that enables lawful presence, credible enforcement, and stable relations at sea.
Footnotes
[1] United Nations Convention on the Law of the Sea pmbl., Dec. 10, 1982, 1833 U.N.T.S. 397.
[2] Id. arts. 2, 56, 87.
[3] Id. arts. 5–14.
[4] Id. arts. 2–3.
[5] Id. arts. 17–19, 25.
[6] Id. art. 33.
[7] Id. arts. 17–26, 52.
[8] Id. arts. 37–44.
[9] Id. arts. 53–54.
[10] Id. art. 92.
[11] Id. arts. 218–219.
[12] Id. art. 56.
[13] Id. arts. 56(2), 58(3).
[14] Id. art. 77.
[15] Id. art. 87.
[16] Id. arts. 92–94.
[17] Id. arts. 136–137.
[18] Id. arts. 192–194.
[19] Id. arts. 279–296; Annexes V and VII.