Vishwamitra Concepts #014: The Basics of International Maritime Law

Vishwamitra Concepts Issue #014

The treaty that provides the central legal framework for the world's oceans has 172 parties. The United States signed it in 1982 but has never ratified it, yet regularly invokes many of the law-of-the-sea principles reflected in the convention when asserting navigational rights.

By Santhosh Vishwamitra

Strategic Briefing

International maritime law is built around a foundational instrument: the 1982 United Nations Convention on the Law of the Sea, or UNCLOS. It divides ocean space into different legal zones, each carrying different rights for coastal states and different freedoms for other states. Most explanations stop at naming those zones. What they often omit is the part that matters for understanding current maritime tensions: how legal text interacts with geography and state capability, where enforcement becomes difficult, and what consequences follow for energy security, undersea infrastructure, shipping and great-power competition.

This piece delivers a working mental model, not a terminology list.

The Paradox at the Foundation

The United States has never ratified UNCLOS. It did, however, sign the convention in 1982. That distinction matters. The US operates one of the world's most capable ocean-going navies, conducts an extensive Freedom of Navigation program, and regularly relies on principles reflected in UNCLOS when asserting navigational rights. At the same time, because it has not ratified the convention, it is not a party to UNCLOS in the same way as states that have ratified it.

The US position is not simply that the entire convention binds every state as customary international law. Rather, the United States has long maintained that many traditional law-of-the-sea rules reflected in UNCLOS constitute customary international law and therefore apply independently of treaty ratification. This distinction is important when interpreting American maritime policy.

China presents a different problem. China signed and ratified UNCLOS, but it rejected the 2016 South China Sea arbitration award issued under Annex VII of the convention. The tribunal proceeded despite China's non-participation and issued its final award in July 2016. China maintains that the arbitration was improperly brought and has rejected the award's conclusions.

Neither example means that international maritime law is meaningless. They reveal something more important: the maritime legal regime is not administered by a single global authority capable of guaranteeing compliance everywhere. States interpret provisions, contest claims, use legal institutions, and sometimes refuse to accept legal conclusions that conflict with their strategic interests.

The useful question about a maritime dispute is therefore not only "What does UNCLOS say?" It is also "What exactly is being claimed, what legal provision supports that claim, and what happens if the claimant or another state refuses to accept the competing interpretation?"

The Zone Architecture

UNCLOS divides maritime space into different legal zones measured from a coastal state's baseline, the line from which maritime distances are calculated. In the ordinary case, the baseline follows the low-water line along the coast. In specific geographic circumstances, including deeply indented coastlines or fringes of islands, straight baselines may be used subject to the convention's conditions.

Zone	Distance from Baseline	Coastal State Holds	Other States Retain
Internal Waters	Landward of baseline	Broad sovereignty, subject to specific UNCLOS rules	No general right of passage comparable to innocent passage in the territorial sea
Territorial Sea	0 to 12 nm	Sovereignty over the territorial sea, its seabed and subsoil, and the airspace above	Right of innocent passage, subject to UNCLOS conditions; submarines must navigate on the surface and show their flag
Contiguous Zone	12 to 24 nm	Specified enforcement powers relating to customs, fiscal, immigration and sanitary laws	Freedom of navigation and overflight, subject to the applicable legal regime
EEZ	Up to 200 nm	Sovereign rights over living and non-living resources, plus jurisdiction over specified matters such as artificial islands, marine scientific research and environmental protection	Freedom of navigation, overflight and other internationally lawful uses of the sea related to those freedoms
Continental Shelf	Normally at least 200 nm where the legal conditions are met, and potentially farther under Article 76	Exclusive rights over natural resources of the seabed and subsoil	Freedoms relating to the overlying water remain governed by the applicable maritime regime
High Seas	Beyond areas of national jurisdiction	No state may claim sovereignty over the High Seas	Freedom of navigation, overflight and other freedoms recognized by international law, subject to applicable rules

The table looks orderly. Maritime practice is not. The most consequential disputes often arise where different legal regimes overlap with competing strategic interests, particularly around territorial seas, internationally used straits, EEZ resource rights and the activities foreign military vessels may conduct in another state's EEZ.

One distinction is especially important. The High Seas are not the same thing as the Area. The High Seas concern waters beyond national jurisdiction. The Area refers to the seabed and ocean floor and their subsoil beyond the limits of national jurisdiction. The Area is governed by a separate regime under UNCLOS and is subject to the principle that its resources constitute the common heritage of humankind.

Where Text Meets Geography

The zone framework above is easiest to understand on a simple coastline. Real coastlines contain islands, reefs, straits, submerged features and neighbouring states whose maritime claims may overlap. Each geographic complication can change the legal analysis.

Baselines and jurisdictional expansion. UNCLOS permits straight baselines in defined geographic circumstances. The legality of a particular baseline depends on whether it satisfies the convention's requirements. States sometimes draw baselines that neighbouring states consider excessive, and those disagreements can affect the maritime areas treated as internal waters or measured from the baseline.

Overlapping EEZs and unresolved delimitation. When two states are less than 400 nautical miles apart, their potential 200 nautical mile EEZs overlap. UNCLOS establishes a framework for reaching an equitable delimitation agreement, but the treaty does not automatically produce a final maritime boundary for every pair of neighbouring states. The East China Sea is one example of a maritime area where competing claims and unresolved delimitation intersect with significant resource and strategic interests.

The island, rock and low-tide elevation distinction. UNCLOS distinguishes between islands capable of generating maritime zones and rocks that cannot sustain human habitation or economic life of their own. Such rocks are not entitled to an EEZ or continental shelf. Low-tide elevations have a different legal status and generally do not generate maritime zones of their own. These distinctions became central to the 2016 South China Sea arbitration.

The tribunal concluded that none of the Spratly Islands features qualified as an island capable of generating an EEZ on the basis of the criteria it applied. China rejected the tribunal's conclusions and continues to dispute the award.

The Enforcement Gap

UNCLOS establishes rights, obligations and dispute-settlement procedures. It does not create a single global enforcement authority capable of guaranteeing that every state will comply with every maritime ruling.

This distinction matters most for states with limited maritime enforcement capacity. A small island state may possess a legally recognized EEZ covering a very large area while having only a small number of patrol vessels, limited surveillance coverage and restricted resources for prosecuting violations. The legal entitlement remains real. The ability to exercise it consistently is another matter.

This is particularly visible in fisheries. Illegal, unreported and unregulated fishing can occur across large EEZs where coastal authorities lack the resources to monitor every vessel. International assistance, regional fisheries organizations, satellite monitoring and cooperation with other states can narrow the gap, but geography makes complete enforcement difficult.

For larger states with capable coast guards and navies, the same legal entitlement can be much more operationally significant. This does not mean that military capability creates legal rights. It means that capability affects a state's ability to monitor, enforce and defend rights that international law already recognizes.

ITLOS and Annex VII arbitral tribunals can issue legally significant decisions under the UNCLOS dispute-settlement system. Their decisions do not come with a worldwide enforcement service. Compliance therefore depends on the legal obligations of the parties, the applicable procedures, diplomatic pressure, domestic implementation and, in some circumstances, the willingness of other states to respond to non-compliance.

Myth: Freedom of navigation operations are simply naval vessels travelling through international waters, where every ship is automatically entitled to pass.

Reality: FONOPs are deliberate legal and operational assertions. When a naval vessel conducts a FONOP in an area where another state has made a contested maritime claim, the operation is intended to communicate that the conducting state considers the claim excessive under international law. The precise route, conduct and legal rationale depend on the claim being challenged.

Second-Order Consequences

The maritime regime matters for much more than fishing rights and shipping lanes. Three consequences deserve particular attention.

Energy security and seabed resources. The continental shelf regime gives coastal states exclusive rights to explore and exploit natural resources of the seabed and subsoil. Where the geological and legal requirements are satisfied, a coastal state's continental shelf may extend beyond 200 nautical miles. States seeking recognition of the outer limits of an extended continental shelf can make submissions to the Commission on the Limits of the Continental Shelf.

The Arctic illustrates why this process matters strategically. Russia, Canada, Denmark through Greenland and Norway have made or pursued submissions relating to extended continental shelf areas in the Arctic. The region contains substantial estimated petroleum resources, although estimates of undiscovered resources are inherently uncertain and should not be treated as guaranteed reserves.

Undersea cable vulnerability. More than 99 percent of international data flows travel through submarine telecommunications cables. The current global network contains hundreds of cable systems connecting continents and national networks. The infrastructure is vulnerable to natural hazards, ageing, fishing activity, anchoring and other forms of physical disruption. The strategic importance of these cables has grown faster than the public understanding of their vulnerability.

UNCLOS contains provisions governing the laying and protection of submarine cables, including obligations concerning damage to cables and freedoms to lay cables in areas where those freedoms apply. The treaty was not designed around today's dependence on globally interconnected digital infrastructure, however, so contemporary governments and industry are increasingly focused on resilience, repair capacity, route diversity and protection of critical subsea infrastructure.

Chokepoint leverage. Internationally used straits can have enormous strategic importance because they connect areas of the sea that would otherwise require much longer routes. UNCLOS's transit passage regime is designed to preserve passage through qualifying international straits while also establishing duties for ships and aircraft exercising that right.

The Strait of Hormuz is a major example. Its importance to global energy markets means that legal arguments over navigation through the strait have consequences far beyond the immediate region. The practical security of such passages depends not only on treaty rules but also on the willingness and ability of states to preserve freedom of navigation.

Where States Actually Disagree

One of the most consequential unresolved interpretive questions concerns what foreign military vessels may lawfully do inside another state's EEZ.

The United States and several other maritime powers maintain that the EEZ preserves important freedoms of navigation and other internationally lawful uses of the sea for all states. They generally reject the proposition that a coastal state has a general right to prohibit foreign military operations in its EEZ.

China and several other states have taken a more restrictive position regarding certain foreign military activities in their EEZs, particularly activities such as military surveys or intelligence-related operations that they regard as inconsistent with the coastal state's rights and interests.

Both sides point to different provisions and principles within UNCLOS. The coastal-state position emphasizes the special legal regime of the EEZ and the rights and jurisdiction expressly granted to the coastal state. The opposing position emphasizes the preservation of navigation and other lawful uses for all states.

This disagreement matters because it connects a technical legal question to military strategy. A state that accepts broad foreign military freedom in another state's EEZ has more room for surveillance and naval operations close to another country's coastline. A state that adopts a more restrictive interpretation gains a stronger legal basis for challenging those activities.

UNCLOS therefore provides the framework for the dispute without eliminating every disagreement about how the framework should be interpreted.

How Does UNCLOS Dispute Settlement Actually Function, and Where Does It Break Down?

UNCLOS provides several mechanisms for compulsory dispute settlement, including the International Tribunal for the Law of the Sea, the International Court of Justice, Annex VII arbitration and, for certain specialized disputes, Annex VIII arbitration. States may make declarations concerning their preferred procedures, while Annex VII arbitration can operate as the default mechanism in circumstances specified by the convention.

The Philippines used Annex VII arbitration when it initiated proceedings against China in 2013. China did not participate in the proceedings and maintained that it did not accept the arbitration. The tribunal nevertheless considered the case and issued awards on jurisdiction and admissibility in 2015 and on the merits in 2016.

The 2016 award addressed questions concerning historic rights, maritime entitlements generated by features, and the legality of certain Chinese activities under UNCLOS. China rejected the award and continues to maintain that the arbitration should not have proceeded.

The case demonstrates both the strength and limitation of international maritime adjudication. A tribunal can produce an authoritative legal determination under the applicable treaty framework even when one party refuses to participate. That does not automatically create a mechanism capable of physically compelling compliance.

Core Principles

Several principles define how the maritime regime operates in practice.

International maritime law is rules-based, but it is not centrally enforced. UNCLOS establishes detailed rights and obligations and provides dispute-settlement mechanisms. It does not create a global coast guard with authority to enforce every provision against every state.

Geography shapes legal outcomes. Islands, reefs, straits, baselines and the distance between neighbouring coasts can determine which maritime rules apply and what entitlements are available.

Capability affects implementation. A legal entitlement and the practical ability to exercise that entitlement are different things. Surveillance, patrol capacity, courts, diplomatic support and maritime infrastructure can determine how effectively a state uses rights that international law recognizes.

Legal ambiguity can become strategically important. Some UNCLOS provisions leave room for competing interpretations. States may therefore contest not only what another state is doing, but what the treaty permits that state to do. The resulting disputes can become part of broader military and diplomatic competition.

Legal authority and physical control are not the same thing. A tribunal can clarify a legal question without changing the balance of power at sea. Conversely, a state can exercise physical control over an area without that control automatically establishing a lawful maritime entitlement.

Strategic Takeaways

UNCLOS provides the core legal architecture for maritime zones, navigation, resources and dispute settlement, but it does not create a centralized global enforcement authority.
The United States signed UNCLOS but has not ratified it. It nevertheless regards many traditional law-of-the-sea rules reflected in the convention as customary international law.
The High Seas and the Area are separate legal regimes. The common-heritage principle applies to the Area, not to the High Seas.
Freedom of Navigation Operations are deliberate legal and operational assertions designed to challenge specific maritime claims.
The military-activities-in-the-EEZ question remains one of the major interpretive disputes in contemporary maritime law.
Undersea telecommunications cables have become strategically important infrastructure, carrying more than 99 percent of international data flows.
International law establishes maritime rights, but geography, institutional capacity and state capability strongly influence how those rights operate in practice.

The Lexicon

UNCLOS : United Nations Convention on the Law of the Sea (1982). The principal international treaty establishing a comprehensive legal framework for the oceans and seas.
Baseline : The line from which maritime zones are measured. It normally follows the low-water line, subject to specific rules permitting other methods in defined geographic circumstances.
Innocent passage : The right of foreign ships to pass through a state's territorial sea while meeting the conditions established by UNCLOS. Submarines must navigate on the surface and show their flag.
Transit passage : The navigation regime applying to qualifying straits used for international navigation. Ships and aircraft retain a right of continuous and expeditious passage while complying with applicable rules.
EEZ : Exclusive Economic Zone. A zone extending up to 200 nautical miles from the baseline where the coastal state has sovereign rights over natural resources and jurisdiction over specified matters.
Continental Shelf : The seabed and subsoil over which a coastal state has exclusive rights to natural resources. The legal continental shelf may extend beyond 200 nautical miles where the conditions of UNCLOS Article 76 are satisfied.
High Seas : Areas of the sea beyond national jurisdiction. No state may claim sovereignty over the High Seas.
Area : The seabed and ocean floor and their subsoil beyond the limits of national jurisdiction. Its mineral resources are governed by the UNCLOS common-heritage regime.
FONOP : Freedom of Navigation Operation. A deliberate operation intended to challenge a specific excessive maritime claim and demonstrate a particular interpretation of navigational rights.
ITLOS : International Tribunal for the Law of the Sea. A judicial body established under UNCLOS and based in Hamburg, Germany.
Annex VII arbitration : An arbitral procedure under UNCLOS that can serve as the default compulsory dispute-settlement mechanism when the convention's applicable conditions are met and the parties have not agreed on another forum.

Check Your Understanding

Q1. A foreign fishing vessel enters State A's EEZ without permission and harvests fish. Has it violated UNCLOS?

Generally, yes. The coastal state has sovereign rights over the living resources of its EEZ. Fishing without the coastal state's authorization can therefore violate those rights. The practical ability to detect and prosecute the violation is a separate question.

Q2. A foreign navy conducts military survey operations in State B's EEZ without notification. Is this permitted?

The legal answer is contested. Some states, including the United States, interpret the EEZ provisions as preserving substantial freedom for foreign military activities. China and several other states take a more restrictive view of certain military activities in their EEZs. UNCLOS does not provide a single universally accepted interpretation that has eliminated the dispute.

Q3. Can a state reject an international maritime arbitration award that goes against it?

A state can refuse to accept or comply with an award in practice, as China has done regarding the 2016 South China Sea arbitration. That does not erase the award or prevent other states from treating it as an authoritative legal determination within the applicable legal framework.

Think Deeper

The United States signed UNCLOS in 1982 but has not ratified it, while maintaining that many traditional law-of-the-sea rules reflected in the convention are customary international law. At the same time, states that have ratified UNCLOS can still dispute the interpretation of its provisions and, in some cases, reject the practical consequences of international rulings. What does this reveal about the relationship between treaty membership, customary international law, state power and international legal authority?

The Vishwamitra Verdict

UNCLOS has achieved something remarkable. It transformed a historically fragmented body of maritime practice into a broadly accepted legal architecture covering territorial seas, exclusive economic zones, continental shelves, navigation, resources, environmental obligations and dispute settlement.

Its importance does not come from eliminating every dispute. It comes from establishing the framework within which most of those disputes are argued.

Its limitations are equally important. UNCLOS does not create a centralized enforcement authority capable of guaranteeing compliance everywhere. States with limited maritime capacity can struggle to exercise rights over enormous maritime zones. States with major naval and coast-guard capabilities can enforce their claims much more effectively. Legal entitlement and practical control therefore remain related but distinct concepts.

The convention also contains areas of genuine interpretive disagreement. The question of foreign military activity in another state's EEZ is one of the clearest examples. Different states read the relationship between coastal-state rights and navigation freedoms differently, and those interpretations have direct strategic consequences.

The same is true beyond naval competition. Continental shelf claims influence access to seabed resources. International straits affect global trade and energy security. Submarine cables carry more than 99 percent of international data flows, making the security and resilience of subsea infrastructure an increasingly important strategic issue.

The maritime legal regime is therefore neither a perfect rulebook nor an empty diplomatic exercise. It is a functioning international framework whose rules matter greatly, whose institutions can produce consequential legal decisions, and whose effectiveness ultimately depends on how states interpret, implement and defend the rights and obligations created by the system.

That is the essential mental model. UNCLOS tells states what maritime rights and responsibilities look like. Geography determines where those rules apply. Institutions interpret them. And state capability often determines how effectively those rules operate in the real world.

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We do not follow the "breaking news" race. Instead, we focus on delivering thoughtful analysis and meaningful perspective on important developments.

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Sources & Reference Material

UNCLOS Treaty Status : United Nations Treaty Collection UNCLOS Overview : UN Division for Ocean Affairs and the Law of the Sea International Tribunal for the Law of the Sea : Judgments, Orders and Advisory Opinions South China Sea Arbitration : Permanent Court of Arbitration Case Repository Global Connectivity Report 2025 : International Telecommunication Union Submarine Cable Resilience : International Telecommunication Union

Santhosh Vishwamitra

A developer, analyst, and the Founder & Editor of Vishwamitra Chronicles, dedicated to independent, evidence-based research on geopolitics, science, and history. - About the Author

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