In an era marked by geopolitical fragmentation and open challenges to international norms, the relevance of international law is often questioned. Yet it is precisely under such conditions that international law is most significant. To that end, understanding the institutions that interpret and articulate international law—particularly in moments of strain—is essential. One such institution is the United Nations International Law Commission (ILC), which occupies a unique position in the international legal order.
This post is the nineth in a multi-part series connected to my work as an adjunct professor at American University, Washington College of Law, where I am teaching an upper-level practicum on the ILC. The aim of this series is to make the institutional role, working methods, and legal significance of the ILC more accessible to readers beyond the classroom.
As always, if there’s something you’d like to see added, clarified, or explored further, I’m happy to hear from you!
Introduction
Continuing on from last week’s discussion of the Commission’s programme of work, this week’s post will dive into the natural next question: what has the Commission actually worked on?
The Commission organizes its topics under ten thematic fields of public international law,[1] which collectively represent the landscape of issues it has been asked—or has chosen—to address since its first session in 1949.[2] These categories are not rigid. Some topics even straddle multiple fields. However, together, each provide a useful framework for understanding both the breadth of the Commission’s work and how its priorities have shifted over the decades.
The Ten Fields
The Commission’s topics fall under ten overarching thematic fields:
- Sources of International Law
- Subjects of International Law
- Succession of States
- State Jurisdiction and Immunity from Jurisdiction
- Law of International Organizations
- Position of the Individual in International Law
- International Criminal Law
- Law of International Spaces
- Law of International Relations
- Settlement of Disputes.
This post will address each of these categories in turn.
Sources of International Law
This is, by some measure, the Commission’s most prolific field. The law governing how international law is made, identified, and applied has occupied the Commission almost continuously since its founding. The topics it has produced have also had an outsized influence on international legal practice.
The Commission’s earliest work in this field began in 1949 with an effort to make evidence of customary international law more readily available (1949–1951). This was the beginning of one of the Commission’s recurring preoccupations: not just making law, but making law legible. That work was followed by reservations to multilateral conventions (1951), extended participation in general multilateral treaties concluded under the League of Nations (1963), and the law of treaties (1950–1966). The law of treaties project ultimately became the “Vienna Convention on the Law of Treaties”,[3] which is widely regarded as one of the Commission’s most consequential contributions to international law.
The Commission returned to treaty-related topics repeatedly in the subsequent decades: the most-favoured-nation clause, addressed in two separate parts (1968–1978, 2009–2015); treaties between States and international organizations, or between two or more international organizations (1971–1982); review of the multilateral treaty-making process (1978); reservations to treaties (1995–2011); effects of armed conflicts on treaties (2005–2011); subsequent agreements and subsequent practice in treaty interpretation (2009–2018); and the provisional application of treaties (2012–2021).
The Commission has also engaged with some of the most conceptually ambitious questions in this field. Its work on the fragmentation of international law (2002–2006) confronted the proliferation of specialized legal regimes—e.g., trade law, human rights law, environmental law—and the tensions that arise when they pull international law in different directions. Its work on identifying customary international law (2012–2018), which included guidelines for identifying sources of law under ICJ Statute, Article 38(1)(b), and peremptory (“jus cogens”)[4] norms (2015–2022) have also become standard reference points for practitioners, courts, and scholars.
Three topics in this field remain active today: general principles of law (2018–present), which aims to provide guidelines for identifying sources of law under ICJ Statute, Article 38(1)(c); subsidiary means for the determination of rules of international law (2022–present), which aims to provide guidelines for identifying sources of law under ICJ Statute, Article 38(1)(d); and non-legally binding international agreements (2023–present),which addresses the growing universe of political commitments and “soft law” instruments that shape State behavior without being formally binding.
Subjects of International Law
This is the shortest entry in the Commission’s catalogue. The Commission took up the fundamental rights and duties of States in 1949, but discontinued the effort by 1950. The topic proved too politically contested to yield workable conclusions, and the Commission has not returned to it since. It is a useful early reminder that not every item that makes it onto the Commission’s active programme of work ultimately produces a result—and that the political temperature around a topic can determine its fate as much as its legal content.
Succession of States
When States merge, dissolve, or have their territory reorganized, a host of legal questions arise. What happens to the predecessor State’s treaty obligations? What about its debts and assets? Do its nationals automatically become nationals of the successor State? How about State responsibility?
The Commission first took up succession of States and governments in 1963, eventually subdividing the topic into more manageable components. Work on succession in respect of treaties (1969–1972, 1974–1978) led to the “Vienna Convention on Succession of States in Respect of Treaties”. Work on succession in respect of matters other than treaties (1969–1981) addressed the thornier questions of State property, archives, and debt, and led to the “Vienna Convention on Succession of States in respect of State Property, Archives and Debts”.
Later, the Commission addressed nationality in the context of succession (1995–1999), producing draft articles that remain an important reference for understanding the nationality consequences of State dissolution and unification. The timing of this topic is particularly interesting: with the dissolution of the Soviet Union in 1991, the question of nationality in the context of succession became particularly pressing for the international community, requiring an immediate answer.
Most recently, the Commission added succession of States in respect of State responsibility (2017–present), asking what happens when a successor State inherits responsibility for internationally wrongful acts committed by its predecessor. That topic is currently active, though it is in the process of being discontinued.[5]
State Jurisdiction and Immunity from Jurisdiction
Two topics are included in this category, both of which are closely related in subject matter and significance. The first, jurisdictional immunities of States and their property (1979–1999), produced the draft articles that served as the basis for the United Nations Convention on Jurisdictional Immunities of States and Their Property, adopted by the General Assembly in 2004.[6]
The second, immunity of State officials from foreign criminal jurisdiction (2007–present), is one of the Commission’s most contested ongoing topics. It asks a fundamental question: when, if ever, can a foreign court exercise criminal jurisdiction over an official acting on behalf of a State? The answer has enormous implications for accountability, sovereignty, and the relationship between international criminal law and the traditional rules of State immunity. The contentious nature of the topic may also explain why it is currently the oldest topic on the Commission’s active agenda, having been discussed for almost two decades now.
Law of International Organizations
The Commission’s work in this field is reflective of the increase in legal complications caused by the growing number of international organizations over the past several decades. Early work addressed the representation of States in their relations with international organizations (1958–1971) and the status, privileges, and immunities of international organizations and their personnel (1958–1992), the latter of which was ultimately discontinued before reaching completion.
Two related projects are also of relevance. The Commission’s work on the responsibility of international organizations (2002–2011) analyzed the legal framework for State responsibility when an international organization, rather than a State, caused harm. Likewise, the Commission’s current work on the settlement of disputes to which international organizations are parties (2022–present) is tackling the procedural question of how such disputes can be resolved when the traditional mechanisms for State-to-State dispute settlement may not apply.
Position of the Individual in International Law
For most of international law’s history, individuals were not considered subjects of the legal order in any meaningful sense—only States were. The Commission’s work in this field reflects the slow but significant shift toward recognizing that individuals have legal standing and rights under international law, even if that recognition has come unevenly and incompletely.
Early work on nationality, including statelessness (1951–1954), addressed the foundational question of who belongs to a State and what happens to those who belong to none. The Commission also took up the right of asylum in 1950 and 1960, but ultimately discontinued the effort. More recently, it addressed the protection of persons in the event of disasters (2007–2016) and the related topic of expulsion of aliens (2005–2014)—both of which deal with the vulnerable position of individuals caught in circumstances where States exercise significant discretionary power over their fates.
International Criminal Law
The Commission’s work in this field has played a significant role in developing international criminal law as we know it today.
It was through the Commission, in the early years after its founding, that the international community first attempted to systematize the idea that certain acts constitute crimes under international law, regardless of what domestic law may say. The Commission’s 1949–1950 work on formulating the Nuremberg (aka “Nürnberg”) Principles helped consolidate the legal legacy of the post-World War II tribunals into a set of propositions the international community could recognize as authoritative.[7] Its later work on the question of international criminal jurisdiction (1949–1950) and on defining aggression (1951) also helped moved the field of international criminal law forward, though the aggression question was eventually incorporated into other Commission topics.
The Commission then spent decades on a draft code of “offences”—which were later rephrase to “crimes”—against the peace and security of mankind (1949–1951 and 1953–1954 for Part I; 1982–1996 for Part II). The 1982–1996 portion of this project also included drafting a statute for an international criminal court, which served as a basis for the negotiations that produced the Rome Statute of the International Criminal Court in 1998.
More recent work in this field includes the obligation to extradite or prosecute (aut dedere aut judicare) (2006–2014), which—in normal human speak—means “when you catch a criminal, you either need to prosecute them or hand them over to someone who will”;[8] crimes against humanity (2014–2022), which produced a set of draft articles now under consideration as the basis for a new convention; and prevention and repression of piracy and armed robbery at sea (2022–present), which is currently in its early stages.
Law of International Spaces
International spaces — broadly understood as areas beyond any single State’s national jurisdiction, including the high seas, international waterways, and shared natural resources — have been a recurring focus of the Commission’s work.
Oceans and Seas. The Commission’s work on the law of the sea in the 1950s—addressing both the high seas (1950–1956) and the territorial sea (1950, 1952–1956)—was foundational to the development of modern maritime law, feeding into the four 1958 Geneva Conventions on the Law of the Sea and eventually contributing to the framework that preceded the 1982 United Nations Convention on the Law of the Sea (often referred to as “UNCLOS” or “LOS”). In 1960, the Commission also took up the topic of the juridical régime of historic waters, including historic bays, but it ultimately discontinued the topic after only one year of discussion.
International Watercourses. The Commission next addressed the law of the non-navigational uses of international watercourses (1971–1994), producing draft articles that became the basis for the 1997 Convention on the Law of the Non-Navigational Uses of International Watercourses.
Shared National Resources. Work on shared natural resources was divided between transboundary aquifers (2002–2010) and oil and gas (2002–2010), though the latter was discontinued.
Environment and Climate Change. The Commission’s most recent work in this field has focused significantly on protecting the environment and addressing the impacts of climate change. These include protection of the atmosphere (2013–2021), and protection of the environment in relation to armed conflicts (2013–2022). Additionally, in the 2025 session, the Commission completed its work on sea-level rise in relation to international law (2019–2025), which addressed the profound legal consequences of climate-change-related sea-level rise on statehood, maritime boundaries, and the rights of affected populations.
Law of International Relations
Aside from sources of international law, this is the Commission’s second most prolific area of work. Through these topics, the Commission has sought to clarify the rules that govern how States and their representatives interact on a day-to-day basis.
The Commission’s foundational work here—on diplomatic intercourse and immunities (1953–1958) and consular intercourse and immunities (1955–1961)—served as the basis for the 1961 Vienna Convention on Diplomatic Relations (aka the “VCDR”) and the 1963 Vienna Convention on Consular Relations (aka the “VCCR”), respectively. These two conventions govern the legal status of every embassy and consulate in the world, and are both almost universally ratified (currently there are 193 UN member States, 193 of which are parties to the VCDR and 182 of which are parties to the VCCR).
The Commission’s later work in this field addressed special missions (1960, 1962–1967), which served as the basis for the Convention on Special Missions and its Optional Protocol concerning the Compulsory Settlement of Disputes; the protection of diplomatic agents and other internationally protected persons (1972), which served as the basis for the Convention on the Prevention and Punishment of Crimes Against Internationally Protected Persons, including Diplomatic Agents; the status of the diplomatic bag and courier (1977–1989); and diplomatic protection (1997–2006).
One of the most important topics in this field is the Commission’s work on State responsibility. Addressed intermittently from 1954 to 2001, the Commission produced the Articles on the Responsibility of States for Internationally Wrongful Acts—commonly known as “ARSIWA” or the “ASR”—which, while not a treaty, have become one of the most cited and influential documents in international legal practice.[9] The Commission also undertook an extended effort on international liability for injurious consequences arising out of acts not prohibited by international law (1974, 1979–2001), which was eventually subdivided to address the prevention of transboundary harm from hazardous activities (1974, 1979–2001) and the international liability in case of loss from such harm (1997–2001).
In this field, the Commission has also worked on unilateral acts of States (1997–2006), responsibility of international organizations (2002–2011), and the expulsion of aliens (2005–2014). The Commission’s two newest topics in this field—due diligence in international law (2025–present) and compensation for the damage caused by internationally wrongful acts (2025–present)—were both added to the active programme in 2025 and remain in their earliest stages.
Settlement of Disputes
When States or international organizations find themselves in conflict, how those disputes get resolved is just as important as the substantive rules that govern the underlying disagreement. The Commission has returned to this theme several times, and while the number of topics in this category is relatively small, the influence of its work has been anything but.
The Commission’s earliest contribution came through its work on arbitral procedure (1950–1953, 1956–1958), which produced a set of model rules that went on to heavily shape the development of international arbitration as we know it today. Decades later, the Commission undertook a general debate on the peaceful settlement of disputes (2010–2011), though that discussion did not produce a formal outcome.
The Commission’s most recent topic in this field reflects a gap that the modern international legal order has been slow to address: what happens when an international organization—rather than a State—is a party to a dispute, and the standard State-to-State mechanisms simply do not apply? That is the question driving the Commission’s ongoing work on the settlement of disputes to which international organizations are parties (2022–present), a topic as technically complex as it is practically urgent.
A Note on Discontinued Topics
Not every topic the Commission has taken up has reached a conclusion. Several have been discontinued along the way: the fundamental rights and duties of States, the right of asylum, the juridical régime of historic waters, and shared natural resources (oil and gas) among them.
Discontinuation is not failure in any simple sense. It can reflect changed political circumstances, a recognition that the topic is better addressed by another body, or a judgment that the available legal material is insufficiently developed at that moment in time. The Commission’s willingness to walk away from a topic is itself part of its institutional character: unlike a legislative body that must produce output, the Commission can conclude that the best result is no result at all.
Conclusion
Reading through the full catalogue of topics the Commission has addressed, a few final conclusions stand out:
- First, the Commission has not been static; its priorities have shifted over time from foundational institutional questions (diplomatic relations, the law of treaties, the law of the sea) toward more complex and contested terrain (criminal accountability, environmental law, the legal status of non-legally binding agreements).
- Second, its work is genuinely cumulative: later topics often build directly on earlier ones, and the legal frameworks produced in one generation become the starting point for the next.
- Third, the Commission’s catalogue reveals an institution that has consistently tried to keep pace with a changing world—not always successfully, and not without controversy, but with a sustained seriousness of purpose that is evident across its numerous decades of work.
The Commission’s body of work, spanning ten thematic fields and more than seventy-five years, is the Commission’s enduring legacy, and for anyone trying to understand where international law stands today, it is an indispensable map.
[1] Note that this system of organization is different from that used for the long-term programme of work, which includes three additional topics: law of the environment; law of economic relations; and law of armed conflicts / disarmament. This is likely because these three categories have not resulted in any topics being added to the active programme of work.
[2] See “Analytical Guide to the Work of the International Law Commission”.
[3] The Vienna Convention on the Law of Treaties (1969) entered into force in 1980 and has 118 States parties as of 2025. It governs the formation, interpretation, amendment, and termination of treaties between States, and is routinely cited by international courts and tribunals—even in disputes involving States that have not formally ratified it.
[4] Jus cogens norms, also called peremptory norms, are rules so fundamental that no State can derogate from them even by agreement. The prohibition on genocide, the prohibition on torture, and the prohibition on slavery are classic examples.
[5] See legal.un.org/ilc/guide/3_5.shtml.
[6] The Convention has not yet entered into force, as it has not received the required number of ratifications (30 States parties). As of 2025, only 25 States are parties to the treaty. This serves as a reminder that Commission work, even when adopted as a treaty text by the General Assembly, does not automatically become binding international law.
[7] The Nuremberg Principles affirm, among other things, that individuals can bear criminal responsibility under international law regardless of their domestic legal obligations, and that acting under government orders does not constitute a defense to international crimes.
[8] The obligation to extradite or prosecute project coincided with a International Court of Justice case, Questions relating to the Obligation to Prosecute or Extradite (Belgium v. Senegal), which was instituted on 19 February 2009 and the final judgment on the merits was issued on 20 July 2012. At the time, the international community was grappling with the decades-long effort to prosecute former Chadian dictator, Hissène Habré, for crimes against humanity. For those interested, To Catch a Dictator by Reed Brody gives a wonderful overview of the political situation at the time.
[9] ARSIWA was adopted by the Commission in 2001 and noted, rather than adopted as a convention, by the General Assembly. Despite never becoming a formal treaty, though, ARSIWA is regularly cited by international courts and tribunals, including the International Court of Justice, and by States in their official communications—making it one of the clearest examples of how Commission work can achieve substantial legal influence without ever becoming a formally binding treaty.
Course Materials
References
International Law Commission, https://legal.un.org/ilc/guide/gfra.shtml.
Additional Reading
- Charles Jalloh, The Role and Contributions of the International Law Commission to the Development of International Law (2019) (open access).
- Keri van Douwen, Seventeen men at Lake Success: In search of the International Law Commission (2024) (open access).
Ginger Without Borders 
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