Notes on the History, Development, and Sources of the International Law of the Sea
I. Introduction
The international law of the sea is a vital and vibrant area of international law, encompassing not only the 1982 United Nations Convention on the Law of the Sea (LOSC) but an ever-growing body of additional treaties, frameworks and state practice.
The law of the sea originally emerged from rules concerning the status and control of ocean space, but now extends beyond coastal state sovereignty to address the interests of the international community in the deep seabed, high seas, fish stocks, marine scientific research MSR, military uses of the oceans, and marine environmental protection.
The LOSC and related instruments have made the law of the sea more detailed, expanding in scope and content and interacting with nearly every other mainstream area of international law.
The law of the sea has developed across several phases: early debates on the status of the oceans, the dominance of freedom of the seas, and gradual codification in the twentieth century.
While core treaty law is now relatively settled, ongoing state practice and regulatory efforts address contemporary challenges such as piracy, maritime terrorism, high seas biodiversity protection, and climate change effects on coastlines and ecosystems. The response to climate change may be the greatest test for the law of the sea.
This chapter outlines historical developments from early periods to contemporary times, with particular attention to UNCLOS I, UNCLOS II and UNCLOS III, and to the distinctive sources of international law that animate the law of the sea.
It also considers current challenges explored in later chapters.
II. Historical Development of the International Law of the Sea
There have been legal conceptions of the sea for as long as maritime interaction exists, but the modern international law of the sea was dominated by European practice at least until the mid-twentieth century.
Initially the oceans were seen as maritime highways for trade and commerce; naval power could control access to the oceans and influence adversaries.
Roman law treated the sea as free and common to all, but by the Middle Ages many seas were subject to various forms of appropriation and control by powerful states, with questionable legitimacy.
Early expansive claims included Pope Alexander VI’s bull Inter Caetera and the 1494 Treaty of Tordesillas which drew a meridian through Brazil and allocated the known world to Portuguese and Spanish spheres, affecting adjoining seas.
Observers noted the preposterous pretensions to dominion over the oceans led to the great juridical controversies of mare clausum and mare liberum, from which modern international law arose [Fulton’s assessment].
A. The Grotian View of the Oceans
Hugo Grotius, Mare Liberum (1608), argued that the sea cannot be owned or occupied as it is vast and common to all; the sea is like air and should be open to navigation and fisheries for all.
Grotius observed the sea has been referred historically as res nullius, res communis, and res publica, but he reasoned that occupancy is the basis of ownership, so the sea cannot be owned by any one state.
Grotius linked freedom of the seas to Dutch concerns about East India trade and the threat of Portuguese power, giving broader momentum to the freedom of the seas doctrine.
Debate exists about whether Grotius drew on Roman law, or incorporated Asian state practice in the Indian Ocean and Southeast Asia. The Portuguese and Dutch engaged in and influenced inter-Asian maritime trade for centuries, with knowledge flowing in multiple directions.
Grotius inspired a wide circle of publicists across Europe, who engaged in the so-called battle of the books over the law of the sea.
John Selden later argued for the sovereignty and dominion of England over British seas in Mare Clausum (1635), claiming long-standing state practice of dominion; this stance was ultimately moribund in the face of growing freedom principles.
The Grotian view prevailed, and freedom of the seas became the doctrine of the time and the future, enabling world trade and the expansion of global commerce; this freedom also underpinned imperialism and colonial extraction of resources.
B. The Freedom of the Sea and Territorial Sea Claims
After debates about ownership, the regime of the oceans stabilized from the 17th to the 19th centuries, but concerns about naval power and defense led to reconsideration of absolute freedom of the seas.
Coastal states began to assert rights to control waters adjoining their coasts, giving rise to the concept of a territorial sea as a coastal zone where the adjacent state exercises jurisdiction for security and resource protection (fisheries).
Territorial sea claims were often poorly defined and not easily enforceable without naval power, yet the trend toward a territorial jurisdiction began to emerge and required accommodation within the freedom framework.
C. 1930 Hague Conference
The League of Nations era saw renewed efforts to codify law of the sea and to codify state practice on territorial sea and adjacent zones.
The 1930 Hague Codification Conference, attended by 44 states, failed to produce a treaty on the law of the sea due to dispute over territorial sea breadth and the relationship with a potential contiguous zone.
The 1936 Montreux Convention on Straits regulated transit through the Black Sea, representing a significant development in straits regime.
D. Truman Proclamation
After World War II, the United States issued Presidential Proclamation No 2667 (the Truman Proclamation) in September 1945, asserting jurisdiction and control over the natural resources of the continental shelf subsoil and seabed adjacent to the coast.
The proclamation argued that the continental shelf is an extension of the landmass and naturally appurtenant to the coastal nation, establishing the first substantive offshore resources claim beyond the territorial sea, without restricting navigational freedoms.
It paved the way for similar resource-based claims by other coastal states and influenced later practice on the continental shelf regime.
E. Emergence of Jurisprudence and International Courts
The Permanent Court of International Justice (later ICJ) and other tribunals began to shape law of the sea jurisprudence.
The ICJ's early decisions, such as the Corfu Channel case (1949) and the Fisheries case (1951), tackled navigational rights and straight baselines, contributing to the developing regime of territorial sea, straits, and baselines.
The jurisprudence provided guidance on navigational freedoms, baselines, and related issues that would influence later treaty development.
III. Work of the International Law Commission
The United Nations established the ILC to codify and progressively develop international law, including law of the sea.
In the 1950s the ILC devoted significant attention to the law of the sea, considering theoretical and scientific aspects and views of governments.
In 1956 the ILC reached agreement on draft articles on the law of the sea and supporting commentaries. These draft articles became the starting text for UNCLOS I.
As negotiations for UNCLOS I progressed, the ILC circulated its final draft to member states, eliciting responses and shaping treaty text.
IV. The First United Nations Conference on the Law of the Sea and the Geneva Conventions
UNCLOS I in Geneva (1958) produced four relatively short and complementary treaties, all born from the 25 draft articles of the ILC and its commentaries:
Convention on the Territorial Sea and Contiguous Zone
Convention on the Continental Shelf
Convention on the High Seas
Convention on Fishing and Conservation of the Living Resources of the High Seas
Also agreed was an Optional Protocol concerning the Compulsory Settlement of Disputes arising out of the Law of the Sea Conventions and nine resolutions on miscellaneous matters such as nuclear tests, pollution of the high seas by radioactive materials, coastal fisheries, and historic waters.
A total of 86 states attended the Geneva Conference, making it one of the largest post-war law-making conferences.
Dynamics at UNCLOS I included:
Cold War rivalries influencing security aspects and navigational matters
Emergence of developing states as a significant grouping challenging the North, including landlocked states seeking access rights
Key features of the Geneva conventions:
Territorial Sea and Contiguous Zone: codified customary law; Article 6 left the breadth of the territorial sea undefined; the question of 3 nautical miles vs broader claims remained contentious; Article 7 addressed bays and closing lines; Article 24 defined the contiguous zone up to 12 nautical miles; the regime of innocent passage
Continent Shelf: reflected consolidating state practice and customary international law; outer limits were not precisely defined in Article 1; coastal states had sovereign rights to natural resources of the shelf including sedentary species; Article 6 dealt with delimitation rules
High Seas: treaty-based articulation of freedoms; provisions for flag state nationality; piracy and hot pursuit codified within a declaratory framework
Fishing and Living Resources: the treaty sought to regulate high seas fishing with the aim of conservation and sustainable yield; defined as optimum sustainable yield and maximum supply of resources
UNCLOS I thus laid foundations for a treaty-based framework while recognizing gaps and the ongoing evolution of practice
V. The Second United Nations Conference on the Law of the Sea
UNCLOS II Geneva (1960s) sought to address two main issues: breadth of the territorial sea and limits of the fisheries regime; it did not intend to reopen UNCLOS I, but to adjust these issues.
The conference lasted six weeks and saw two camps: supporters of a six nautical mile territorial sea and supporters of a 12 nautical mile territorial sea; it also considered a compromise proposed by the United States and Canada: a territorial sea of six miles plus a fishing zone of an additional six miles (six plus six).
The compromise failed to secure the two-thirds majority needed for a formal agreement, so UNCLOS II did not produce substantive reforms to the Geneva Conventions.
Despite the lack of agreement, UNCLOS II highlighted major gaps in the legal regime and the need for holistic resolution of multiple issues rather than isolated reforms.
VI. The Third United Nations Conference on the Law of the Sea
UNCLOS III (1973–1982) was a longer, more representative negotiation with 11 negotiating sessions across 585 days in three countries; 151 states attended the final substantive sessions; a large number of observers, including NGOs and international organizations, participated.
UNCLOS III featured a broader and more diverse set of participants, including a strong Group of 77 representing developing states, and landlocked states seeking access rights.
A. Claims to New Maritime Zones in the 1960s
As UNCLOS II collapsed, state practice broadened. Many claims emerged for 12 nm EFZs and more expansive zones up to 50, 100, 200, and 400 nm; European states tended toward 12 nm EFZs (Iceland 1958, Norway 1961).
Latin American states expanded to 200 nm; some African states proposed 130 nm territorial seas;
Bilateral and regional agreements recognized 12 nm fishing zones (examples include UK-Norway 1960; Japan-South Korea 1965; Japan-New Zealand 1967; US-Mexico 1967; Spain-Morocco 1969);
The London Fisheries Convention of 1964 created regional recognition of 12 nm fisheries zones among 12 European states.
B. The Regime of the Deep Seabed
The deep seabed regime was a major concern as technology opened up mineral resource exploitation possibilities on the high seas.
In 1967 Ambassador Arvid Pardo proposed declaring the seabed and ocean floor beyond national jurisdiction as part of the common heritage of mankind; the UN General Assembly (UNGA) established the Sea-Bed Committee, launching the process for a new regime.
A moratorium in 1969 placed a pause on deep seabed resource activities beyond national jurisdiction pending UNCLOS III outcomes.
In 1970 UNGA Resolution 2749 declared the seabed and ocean floor beyond national jurisdiction as common heritage of humankind and called on the Sea-Bed Committee to act as a preparatory committee for UNCLOS III.
C. UNCLOS III Conference Dynamics
UNCLOS III was distinct in its process: no ILC draft articles; protracted nine-year negotiations (1973–1982) with 585 days of negotiating sessions in three countries.
It was far more representative, with accession by a larger number of states and broad participation by observers and organizations.
The conference recognized five regional groups for seating in committees: African, Asian, Latin American, Western European, and Eastern European; the Group of 77 emerged as a major negotiating bloc representing developing states.
The debate reflected a desire to transform post-colonial demands into a concrete set of rules for a new era of ocean governance and resource sharing.
D. The United States Position on Common Heritage and the Deep Seabed
In 1981 the Reagan administration expressed significant reservations about the deep seabed mining regime and common heritage principles, particularly technology transfer obligations.
Despite U.S. concerns, UNCLOS III proceeded to a vote in 1982; the text was adopted with 130 states in favor, 4 against, and 17 abstentions; Israel, Türkiye and Venezuela joined the United States in voting against the text, though this did not prevent the negotiations from concluding.
VII. The United Nations Convention on the Law of the Sea
The LOSC is a comprehensive treaty with 320 articles and nine annexes, establishing a regime for the law of the sea that both codifies settled law and expands new rules and frameworks.
A key addition is the clearer delineation of rights and duties for coastal, flag, and port states, while recognizing that coastal states are not defined in the LOSC but have coastal baselines and zones; flag states have duties under Article 94; port states have enforcement jurisdiction within their ports.
A. Core Provisions
The LOSC comprises 17 Parts; Part I defines terms and concepts via Article 1; Part II on the Territorial Sea and Contiguous Zone; Part III on Transit Passage through international straits; Part IV on Archipelagic States; Parts V and VI on the EEZ and the Continental Shelf; Part VII on the High Seas; Parts VIII and IX on enclosed or semi-enclosed seas and special states; Part X on landlocked and geographically disadvantaged states; Part XI on the Deep Seabed Area and the ISA; Part XII on Protection and Preservation of the Marine Environment; Part XIII on MSR; Part XIV on Development and Transfer of Marine Technology; Part XV on Dispute Settlement; Parts XVI and XVII on general provisions and final clauses.
Territorial Sea: breadth not to exceed 12 ; the contiguous zone extends up to 24 from baselines; innocent passage and navigation through straits clarified; transit through straits recognized in Part III and Part VII implications for archipelagic routes.
Archipelagic States: Part IV recognizes their rights and navigational freedoms through their waters; special provisions for archipelagos.
EEZ and Continental Shelf: coastal states enjoy sovereign rights over resources up to 200 in the EEZ; continental shelf sovereignty covers resources in the shelf up to a minimum of 200 and possibly outer continental shelf beyond that in defined circumstances.
High Seas: regulated freedoms consistent with customary law; authority to declare navigation freedoms, yet with new rights such as constructing artificial islands and conducting MSR in line with the regime.
Deep Seabed and ISA: the Area is governed by the common heritage of humankind principle; ISA oversight of access to seabed resources.
MSR and Technology Transfer: Part XIII and Part XIV address MSR and the transfer of marine technology, balancing coastal state interests with the international community's freedom of discovery.
Dispute Settlement: Part XV provides compulsory dispute settlement mechanisms, including ITLOS as a permanent tribunal, and options for international arbitration; other mechanisms and Annexes supplement dispute settlement procedures.
General Provisions: Parts XVI and XVII emphasize good faith, peaceful use of oceans, and signatures, ratifications, and entry into force.
B. Entry into Force
UNCLOS III concluded in 1982; the LOSC opened for signature on 10 December 1982 and remained open for signature for two years; ratification or accession by 60 states was required for entry into force.
Fiji is noted as the first state to ratify on the day of conclusion; there was initial enthusiasm but concerns about Part XI deep seabed provisions remained among western states.
It took until the early 1990s to accumulate sufficient support for entry into force due to broad concerns about deep seabed governance and institutional costs for state parties.
C. 1994 Implementing Agreement
The 1994 UNGA resolution led to an Implementing Agreement relating to Part XI intended to address concerns raised by the United States and others about the deep seabed regime and ISA governance.
The Implementing Agreement provided that Part XI and the Implementing Agreement be interpreted and applied together as a single instrument, with the Agreement prevailing in case of inconsistency.
Adoption could occur through LOSC ratification or separate procedures for states already party to LOSC; the Agreement ultimately played a crucial role in enabling the LOSC to come into force.
The LOSC entered into force on 16 November 1994; as of January 2023, 167 states and the European Union had accepted the LOSC, while the Implementing Agreement had 151 parties.
There remain a number of non-parties to the LOSC including 14 coastal states; US opposition to the deep seabed regime has switched in policy over time but acceding to the LOSC has not occurred due to domestic considerations; Israel, Türkiye, and Venezuela have also not joined.
D. 1995 Fish Stocks Agreement
The 1995 Fish Stocks Agreement was negotiated to supplement LOSC provisions governing straddling and highly migratory fish stocks, addressing management and conservation beyond national jurisdiction.
Core objective is long-term conservation and sustainable use of straddling and highly migratory stocks; applies the precautionary principle; expands the role of flag, port, and coastal states in enforcement and compliance mechanics; it is to be interpreted and applied in the context of LOSC, ensuring consistency with LOSC principles.
The Agreement entered into force on 11 December 2001 and had 92 state parties as of January 2023.
VIII. Institutional Frameworks
The LOSC created new institutions to implement its provisions and to interact with other international frameworks:
The International Seabed Authority ISA, headquartered in Jamaica, oversees access to and exploitation of seabed resources in the Area and addresses environmental impacts related to seabed mining; implementation of the 1994 Implementing Agreement has allowed ISA to function effectively.
ITLOS, the Permanent International Tribunal for the Law of the Sea, is the main dispute resolution body under Part XV; located in Hamburg; has developed distinctive jurisprudence across multiple law of the sea areas.
The Commission on the Limits of the Continental Shelf CLCS evaluates and makes recommendations on outer continental shelf limits for coastal states; its mandate and operations are detailed in Annex II of the LOSC; unlike ISA and ITLOS, CLCS does not have a permanent seat but operates primarily from the UN Headquarters in New York.
Other important processes and bodies:
Article 319 contemplates meetings of States Parties SPLOS in New York; annual reviews and budgetary matters; the Secretary-General acts as depositary for the LOSC.
The United Nations Open-Ended Informal Consultative Process on Oceans and the Law of the Sea ICP since 2000 has allowed LOSC states to discuss emerging issues informally.
The UNGA routinely reviews LOSC implementation and, in 2017, agreed to convene an Intergovernmental Conference to elaborate an international legally binding instrument ILBI for the conservation and sustainable use of marine biological diversity of areas beyond national jurisdiction BBNJ.
The UN Security Council has adopted resolutions with direct impacts on the law of the sea in specific matters.
Other major UN and international bodies play roles in law of the sea matters, including the IMO, FAO, UNEP, which influence marine pollution, fisheries management, and environmental protection policies.
IX. Sources of the International Law of the Sea
A. Customary International Law
Article 38(1) of the ICJ Statute lists customary law alongside treaty law as a source; customary law remains important in areas not fully articulated in LOSC or where practice has extended treaty provisions. The ICJ has recognized the ongoing role of customary law in the law of the sea, including maritime boundary delimitation.
The North Sea Continental Shelf cases clarified general principles for determining customary norms and have influenced subsequent maritime boundary delimitation through practice and customary law.
B. Treaties and Conventions
Since the four 1958 Geneva Conventions, treaty law has dominated the contemporary LOSC regime; the LOSC is central but interacts with other multilateral and bilateral treaties.
The LOSC has a mixed status: parts of it codify customary law, while others create new rules that extend beyond existing customary practice; some provisions replicate Geneva Conventions, others extend them, and some are novel.
The LOSC supersedes the Geneva Conventions among LOSC State Parties; Article 311(1) states that LOSC prevails between states parties to both instruments; LOSC does not automatically apply between a LOSC party and a Geneva Convention party where both are not LOSC parties.
Other important treaty structures include global and regional multilateral treaties under IMO on marine pollution and regional fisheries treaties; numerous bilateral treaties also govern maritime boundaries.
C. Unilateral Declarations
Two kinds: (i) declarations that extend existing law and state practice, sometimes without full reference to LOSC; the Truman Proclamation is a classic example; (ii) declarations asserting new maritime claims consistent with existing law, reflecting a state's right to claim certain areas under LOSC.
Unilateral declarations influence practice and may be relevant in ICJ cases.
D. Subsidiary Sources of Law
International publicists have greatly shaped the law of the sea, notably Grotius and subsequent publicists; advisory opinions and doctrines have influenced developments.
Decisions of international courts and tribunals have contributed to law of the sea development, including the ICJ Corfu Channel and North Sea Continental Shelf lines of authority and the South China Sea arbitration under Part XV/Annex VII.
Equitable and general principles of law recognized in Article 38(1)(c) ICJ Statute have informed law of the sea developments.
E. Soft Law
Soft law instruments have guided and sometimes become hard law; UNGA resolutions on the deep seabed in 1969 and 1970 reflected common heritage principles; non-binding instruments such as the 1991 UNGA Resolution on Drift-Net Fishing contributed to a global moratorium on certain practices.
Other soft law examples include Agenda 21 (1992) with chapter 17 on protection of oceans; the 1995 FAO Code of Conduct for Responsible Fisheries; the 2001 FAO International Plan of Action to prevent illegal, unreported and unregulated fishing; and the 2009 IMO Code of Conduct on piracy and armed robbery in the Western Indian Ocean and the Gulf of Aden.
Soft law is attractive because it can respond quickly to new issues without the formal treaty process, but may later be codified into hard law where appropriate.
X. Review and Reform of the International Law of the Sea
The LOSC and its network of treaties provide an extensive regime, but gaps and uncertainties remain.
The 1994 Implementing Agreement and the 1995 Fish Stocks Agreement broaden the LOSC framework and address specific issues left unresolved by the conference.
Climate change and other technological advances pose new challenges that may require reform or reinterpretation of LOSC provisions.
Three main pathways for reform are identified:
The 1994 Implementing Agreement mechanism, though unique in origin, demonstrates how agreements can be used to modify or complement LOSC provisions without a full new treaty;
The 1995 Fish Stocks Agreement demonstrates a model for targeted supplementary treaties that align with LOSC principles;
Formal amendments to the LOSC through its amended articles; there are three amendment pathways: (i) general amendments via Articles 312 and 313, (ii) amendments to the deep seabed regime via Article 314 and Annex of the Implementing Agreement, and (iii) potential new international instruments such as ILBI for BBNJ.
The potential for a future Fourth United Nations Conference on the Law of the Sea is discussed as a possible mechanism for comprehensive reform, but there are questions about effectiveness and timing.
The concluding emphasis is on an integrated approach to climate governance and ocean governance involving LOSC and other areas of international law; the LOSC is viewed as a living treaty capable of adapting to new challenges through state practice, new treaties and implementing agreements, and decisions of international courts and tribunals.
The chapter closes with a call for an integrated approach to land, sea, and atmosphere governance and for continuing evolution of the LOSC to respond to climate and other global changes.
XI. Further Reading
Anand RP Origin and Development of the Law of the Sea. The Hague: Martinus Nijhoff, 1983
Additional works and authors listed in the chapter include many prominent scholars in the field of the law of the sea; references include: Armitage, Bashford, Sivasundaram; Bederman; Brown; Churchill & Lowe; Crawford; Harrison; Lay; Lowe & Talmon; O’Connell; Oude Elferink; Treves; Koh and other leading scholars.
Representative bibliographic entries from the chapter include: The Oxford Handbook of the Law of the Sea; Brownlie; The Law of the Sea in various parts; and other foundational and contemporary works cited in the chapter.
Quick reference: key figures and terms (selected)
UNCLOS I, UNCLOS II, UNCLOS III: Geneva, 1958; conference proceedings; leading to the LOSC in 1982
Three main treaty frameworks before LOSC: Territorial Sea and Contiguous Zone, Continental Shelf, High Seas, Fishing and Conservation of Living Resources of the High Seas
Territorial sea breadth discussions: Article 6 of the Geneva Conventions left the breadth undetermined; 12 nm later became widely accepted; later broad debates about wider territorial seas.
Contiguous Zone: up to 12 nm; enforcement of customs, fiscal, immigration, sanitary laws; Article 24 defined the zone
EEZ: up to 200 nm from baseline; established during UNCLOS III; crucial for coastal state resource rights
Continental Shelf: sovereign rights to natural resources in the shelf; Article 1 left outer limits undefined; Article 6 delimitation rules; the regime is based on customary law and codified in the LOSC
Deep Seabed Area and ISA: common heritage of humankind; ISA oversees access to seabed resources and environmental safeguards
MSR and Technology Transfer: Part XIII and Part XIV; balance of discovery rights and coastal state interests
Dispute Settlement: Part XV; compulsory procedures; ITLOS established in 1996
BBNJ ILBI: planned instrument under LOSC for biodiversity beyond national jurisdiction; ongoing process started with 2017 decision to convene an intergovernmental conference
Soft law: UNGA resolutions, Agenda 21, FAO codes, and other non-binding instruments shaping practice and possibly hard law later