UN Convention on the Law of the Sea

You and your friends decided to take an impromptu weekend road trip from the United States to Canada. As you near the border, you get your passport ready, then sit tight while a long line of cars in front of you waits to pass through border security. There are fences, security booths, huge flags, and big signs all around you. You couldn't miss this political border even if you tried!

UN Convention on the Law of the Sea UN Convention on the Law of the Sea

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    But how do political boundaries function at sea? How do we even know where they are? Well, our maritime political boundaries were largely established by the United Nations through the 1982 Convention on the Law of the Sea. Find your sea legs, shipmate—it's time for a maritime adventure.

    UN Convention on the Law of the Sea Definition

    The United Nations Convention on the Law of the Sea (UNCLOS) is an international agreement that describes how sea-going vessels should interact with each other and with marine resources in regional waters and the high seas. The high seas are the parts of the world's oceans that are not under the jurisdiction of any national government—they are international waters.

    UN Convention on the Law of the Sea, UN Convention on the Law of the Sea Definition, High Seas Map, StudySmarterFig. 1 - High seas are in dark blue

    UNCLOS defines everything from freedom of navigation to piracy to pollution to wildlife conservation. But perhaps more relevant to geography, UNCLOS also delineates maritime political and economic boundaries. In other words, UNCLOS provides guidance for what exactly are and aren't the aforementioned high seas. According to the UN, the oceans are the common heritage of humankind, and UNCLOS attempts to find a balance between freedom and sovereignty.

    1982 UN Convention on the Law of the Sea

    Before 1952, countries around the world were using completely different "rulebooks" to determine their own maritime territory and authority. It was in recognition of this that the United Nations held the first Convention on the Law of the Sea. The goal was to establish a common framework for international interactions on and with the oceans.

    The international maritime law we have in place today largely came about as a result of the United Nations' third Convention on the Law of the Sea. This convention lasted from 1973 to 1982 and came into effect in 1994. Over 160 nations participated in this conference, which was held in New York City. The current UNCLOS agreement was created as a result of this convention.

    Signatories to the UN Convention on the Law of the Sea

    UNCLOS has been almost universally adopted by the countries of the world. A whopping 168 parties (including UN members and supranational organizations like the European Union) have signed and confirmed (ratified) both the convention itself and the resultant agreement.

    Fifteen parties have neither signed nor ratified either the convention or the agreement, including Turkey, Israel, and Venezuela. Fourteen additional parties have signed either the convention or the agreement, but not ratified it. The United States falls in this category.

    UN Convention on the Law of the Sea, Signatories UN Convention on the Law of the Sea, UNCLOS Map, StudySmarterFig. 2 - Countries in blue are either parties to UNCLOS or signatories; countries in red are not parties to UNCLOS

    The United States was instrumental in developing UNCLOS but declined to sign the convention or ratify the convention or agreement. The deal breaker? Part XI of UNCLOS created the International Seabed Authority to regulate mining expeditions in international waters. The US saw this as an unnecessary restriction on economic activity.

    Even amongst those who have not signed or ratified UNCLOS, it has become customary international law: they do not regard it as legally binding, but follow it as a matter of good custom. This includes the US, which, ironically, frequently uses the US Navy to enforce UNCLOS regulations.

    UN Convention on the Law of the Sea Summary

    So, what does UNCLOS actually say?

    Countries with maritime borders have sovereignty over a portion of the ocean. The farther out to sea from a country's shore you go, the less economic or political power that country has until you reach the high seas. Distance is typically measured from a coastal baseline, usually based on an average of when the tides are at their lowest level (mean low-water line). These distances are quantified in nautical miles (nm); one nautical mile is about 1.15 miles (1.85 kilometers).

    Official UNCLOS ZoneDistance from the BaselineNational Economic/Political Rights
    Inland WatersInland of the BaselineComplete and total sovereignty.
    Territorial Waters12nmSovereign national territory, similar to land-based political boundaries. Foreign vessels may only enter under unique circumstances.
    Contiguous Zone24nmA country has limited law-enforcement jurisdiction to prevent crimes it believes may cross into territorial waters (customs violations, trafficking, etc.).
    Exclusive Economic Zone (EEZ)200nmA country has sole access to collect all resources within its EEZ, such as via fishing, mining, and fracking.
    The Area (High Seas/International Waters)Beyond 200nmShared by all countries; freedom of navigation by all vessels; restricted economic activity.

    Note that these boundaries also include airspace.

    In addition to the above zones, UNCLOS defines sovereign authority for archipelagic nations and for nations with continental shelves.

    Archipelagic nations, like the Philippines, are comprised of many islands. According to UNCLOS, their zones begin at the baselines of the outermost islands of the archipelago, with waters between the other islands being treated legally similar to territorial waters.

    Island: land above the water capable of supporting human habitation or economic activity—not just a random rock in the middle of the ocean!

    Continental shelves are underwater continuations of landmasses. They are directly connected to a country's territory on dry land. Continental shelves are special in that the UN recognizes a country's exclusive economic access to its continental shelf up to 350nm from the baseline. However, even if a continental shelf extends beyond 350nm, a country's rights do not continue to extend along with it.

    Do We Have to Share?

    What if two countries have overlapping zones? What if a foreign vessel needs to enter a country's territorial waters? Such situations are common in straits, where several countries border the ocean in a relatively small space.

    There are two major issues to resolve: delegation of political and economic rights; and the need for foreign vessels to transit through waters that would normally be territorial waters.

    UNCLOS Median Line

    According to UNCLOS, in the case of overlapping zones, political and economic rights should be demarcated via a median line based on the equidistance principle. This median line divides the countries' territorial waters, contiguous zone, and EEZ (if applicable, respectively) proportionally based on each country's baseline. This means both countries' maritime territories will be truncated, but theoretically, they will be truncated pro rata.

    UN Convention on the Law of the Sea, UN Convention on the Law of the Sea Summary, Equidistance Principle, Media Line, North Sea EEZ map, StudySmarterFig. 3 - The equidistance principle in action in the North Sea

    Transit Passage vs Innocent Passage

    Due to maritime geography, it may be necessary to pass through a country's territorial waters when navigating from one part of the high seas to another.

    Transit passage refers to passing through a strait. Many straits, like the Strait of Hormuz, the Strait of Gibraltar, or the Strait of Malacca, are traffic chokepoints: you simply must pass through them to get from one point to the other, even though doing so technically puts you within territorial waters. Transit passage must be continuous and expeditious. Warships on transit passage, for example, may still conduct basic military exercises, so long as doing so does not hinder their ability to continuously and expeditiously move through the strait.

    UN Convention on the Law of the Sea, UN Convention on the Law of the Sea Summary, Transit Passage, StudySmarterFig. 4 - A cargo ship conducts transit passage in the Strait of Messina

    A vessel can conduct innocent passage when it finds the most logical route from one area of the high seas to another will require that it drive through a country's territorial waters. For example, it may be easier to cut through an archipelago's waters than go all the way around the archipelagic nation. For a vessel to conduct innocent passage, it must cease all economic, military, and research activities.

    Additionally, claiming innocent passage is a tacit acknowledgment of a country's claimed political and economic maritime borders. When these borders conform with UNCLOS, that's usually no big deal. But around the world, countries claim maritime borders not in line with UNCLOS guidelines. Driving through these waters without claiming innocent passage is often seen as a rejection of these claims. Warships are sometimes tasked with conducting freedom of navigation operations (FONOPs) in these areas.

    Since 2014, the People's Republic of China has been constructing artificial islands in the South China Sea. China uses these artificial islands (as well as uninhabitable rocks and atolls) to extend its claimed territorial seas and EEZ in the South China Sea—though Chinese government officials also assert that the entirety of the South China Sea is historic Chinese territory anyway and is not subject to UNCLOS.

    The US Navy frequently conducts FONOPs in the South China Sea to repudiate China's claims.

    What Else Does UNCLOS cover?

    Briefly, UNCLOS also covers the following:

    Submarine Cables

    UNCLOS affirms the right of a country to lay underwater cables, usually for internet connectivity, in its own EEZ.


    UNCLOS affirms that piracy is illegal under international maritime law and empowers convention parties to suppress and deter piracy.

    The Right of Hot Pursuit

    Foreign vessels caught violating UNCLOS zoning guidelines may be pursued and detained by a vessel belonging to the country whose zone was violated. This vessel may even pursue the violator on the high seas, until/unless the violator enters their own or a third party's territorial waters.

    Non-Coastal States and Access to the Sea

    When relevant, landlocked countries may access the EEZ of a country in their region. A coastal state may not block a landlocked country's access to the oceans.

    Economic Exploitation and Marine Conservation on the High Seas

    As mentioned above, the UN regulates economic ventures in international waters . Similarly, the UN is in charge of regulating wildlife conservation and pollution in international waters.

    What about traffic?

    UNCLOS is not to be confused with the International Regulations for Preventing Collisions at Sea (the COLREGs). The COLREGs were also created by the United Nations via the International Maritime Organization. Unlike UNCLOS, the COLREGs explain in detail how traffic is supposed to flow at sea.

    In the United States, the Coast Guard publishes the COLREGs in a book called Navigation Rules and Regulations Handbook, colloquially called the "Rules of the Road." Every United States vessel greater than 12 meters in length is required to have a copy of the Rules of the Road onboard.

    UN Convention on the Law of the Sea - Fisheries

    How does UNCLOS affect the most quintessential nautical career—fishing?

    A fishery is where fish and other aquatic life are caught, harvested, or raised (such as on a fish farm). "Fishery" also refers to the act of catching, harvesting, or farming fish and other aquatic life.

    Coastal states have exclusive rights to fishing in their own EEZ (unless they must share their EEZ with a landlocked country). Existing fishing agreements between countries take precedence over UNCLOS directives. The UN expects and requires that each country regulate fishing in its own waters. Fishermen may also fish on the high seas, so long as they don't violate conservation regulations established by the UN or other states.

    UNCLOS also affirms traditional fishing rights, that is, the right of Indigenous people to maintain their own fisheries.

    UN Convention on the Law of the Sea - Key takeaways

    • The United Nations Convention on the Law of the Sea (UNCLOS) is an international agreement that describes how sea-going vessels should interact with each other and with marine resources in regional waters and the high seas.
    • The current version of UNCLOS was completed in 1982 and went into effect in 1994.
    • The US is not a party to UNCLOS because it objects to some of its economic aspects. However, in practice, the US accepts UNCLOS as customary international law.
    • UNCLOS establishes a system defining the zones over which a coastal nation has sovereignty. This includes territorial waters (12nm from the baseline), the contiguous zone (24nm from the baseline), and the exclusive economic zone (200nm from the baseline).


    1. Fig. 1: Exclusive Economic Zones (https://commons.wikimedia.org/wiki/File:Exclusive_Economic_Zones.svg), by B1mbo (https://commons.wikimedia.org/wiki/User:B1mbo), Licensed by CC BY-SA 3.0 CL (https://creativecommons.org/licenses/by-sa/3.0/cl/deed.en)
    2. Fig. 4: Ro-Ro ship Eurocargo Genova transiting the Strait of Messina (https://commons.wikimedia.org/wiki/File:Ro-Ro_ship_Eurocargo_Genova_transiting_the_Strait_of_Messina_-_20_July_2010.jpg) by Jacopo Werther (https://commons.wikimedia.org/wiki/User:Jacopo_Werther), Licensed by CC BY-SA 3.0 (https://creativecommons.org/licenses/by-sa/3.0/deed.en)
    Frequently Asked Questions about UN Convention on the Law of the Sea

    What does the Law of the Sea Convention mean? 

     The United Nations Convention on the Law of the Sea (UNCLOS) is an international agreement that describes how sea-going vessels should interact with each other and with marine resources in regional waters and the high seas. 

    Should the USA sign the UN Convention on the Law of the Sea? 

    The United States already tacitly accepts the UN Convention on the Law of the Sea as customary international law and even uses the US Navy to help enforce it. As to whether the US should formally sign and ratify UNCLOS, that is for US government officials to decide! 

    When was the UN Convention on the Law of the Sea? 

    The third (and currently applicable) UN Convention on the Law of the Sea took place from 1973 to 1982. It went into effect in 1994. 

    What are the principles of the law of the sea? 

    The United Nations frames the world's oceans as the common heritage of mankind, and the UNCLOS attempts to find a balance between freedom and sovereignty. 

    Why is the US not a part of the United Nations Convention on the Law of the Sea? 

    The US objected to Article XI of UNCLOS, which allows the United Nations to regulate economic activity in international waters. The US insists that this regulatory oversight puts unnecessary restrictions on economic opportunities. 

    Test your knowledge with multiple choice flashcards

    Which of the following BEST describes the UN Convention on the Law of the Sea? 

    Why is the United States NOT a party to UNCLOS? Select the BEST answer.

    Which of the following is the most accurate description of an UNCLOS zone? 


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