A. Executive summary
The International Law Commission (ILC) is close to finalizing its draft conclusions on general principles of law (GPL). These conclusions clarify how GPL are identified and what functions they perform within the international legal system. For investment arbitration, they intersect directly with the framework of the applicable law that investment tribunals may rely upon to settle a dispute.
B. The ILC’s project on general principles of law
The ILC placed “General principles of law” on its program of work in 2018 and appointed Marcelo Vázquez-Bermúdez as Special Rapporteur. In 2023, at its seventy-fourth session, the Commission adopted eleven draft conclusions on first reading, together with detailed commentaries (Report A/78/10).
On first reading, the ILC:
- Confirmed that GPL are a source of international law within the meaning of Article 38(1)(c) of the ICJ Statute (Draft conclusion 1).
- Distinguished GPL derived from national legal systems from GPL formed within the international legal system itself (Draft conclusion 3).
- Explained that GPL can interpret other rules and contribute to systemic coherence, without being hierarchically subordinate to treaties or CIL (Draft conclusions 10-11).
In 2025, the ILC considered the fourth report of the Special Rapporteur and a revised set of draft conclusions on second reading. The Drafting Committee provisionally agreed on the text (now 12 conclusions), but final adoption with commentaries was postponed to the seventy-seventh session (2026) due to time constraints.
C. General principles of law in ICSID, USMCA and CETA
(i) ICSID Article 42 and paragraph 40 of the Report of the Executive Directors
Article 42.1 of the ICSID Convention provides that:
- The tribunal shall decide a dispute in accordance with such rules of law as may be agreed by the parties;
- In the absence of such agreement, it shall apply the law of the Contracting State party to the dispute (including its rules on conflict of laws) and such rules of international law as may be applicable.
Paragraph 40 of the Report of the Executive Directors explains that, in this context, “international law” in Article 42.1 is to be understood in the sense of Article 38.1 of the Statute of the International Court of Justice.
Since Article 38.1 of the ICJ Statute lists “general principles of law recognized by civilized nations” alongside treaties and custom, paragraph 40 confirms that general principles of law are part of the “rules of international law” that ICSID tribunals should apply under Article 42.1.
(ii) USMCA Article 14
Article 14.D.7- “Conduct of the Arbitration”
“7. For greater certainty, […] the investor has the burden of proving all elements of its claims, consistent with general principles of international law applicable to international arbitration.”
Article 14.D.9 – “Governing Law”
“[…]when a claim is submitted under Article 14.D.3.1 (Submission of a Claim to Arbitration), the tribunal shall decide the issues in dispute in accordance with this Agreement and applicable rules of international law.”
(iii) CETA Article 8.31
Article 8.31(1) provides that the investment tribunal shall apply:
“[…] this Agreement as interpreted in accordance with the Vienna Convention on the Law of Treaties, and other rules and principles of international law applicable between the Parties.”
D. General principles of law in investment arbitration practice
Across ISDS fora, investor-State tribunals have relied on GPL in a number of disputes and in different contexts, invoking principles such as:
- Good faith (Amco v Indonesia, Decision on Jurisdiction 25 September 1983, Europe Cement v Turkey, Award, 13 August 2009, Vigotop v Hungary, Award 1 October 2014),
- prohibition of corruption (Wena Hotels v Egypt, Award 8 December 2000), World Duty Free v Kenya, Award 4 October 2006, Krederi v Ukraine, Award 2 July 2018),
- nemo auditur propriam turpitudinem allegans (Inceysa v El Salvador, Award 2 August 2006),
- general principles of contract law including (i) pacta sunt servanda (Amco v Indonesia, Award 20 November 1984, Gardella v Côte d’Ivoire, Award 29 August 1977, Watkins Holdings v Spain, Award 21 January 2020) and (ii) exceptio non adimpleti contractus (Klöckner v Cameroon, Award 21 October 1983, Autopista v Venezuela, Award 23 September 2003),
- estoppel (Amco v Indonesia, Resubmitted Case, Award 5 June 1990, SGS v Pakistan, Decision on Jurisdiction 6 August 2003, Pan American v Argentina, Decision on Preliminary Objections 27 July 2006, Fraport v Philippines I, Award 16 August 2007),
- unjust enrichment (Amco v Indonesia, Resubmitted Case, Award 5 June 1990, SPP v Egypt, Award 20 May 1992),
- full compensation (Amco v Indonesia, Award 20 November 1984),
- general principles of due process (Amco v Indonesia, Award 20 November 1984),
- burden of proof (AAPL v Sri Lanka, Award 27 June 1990, Salini v Jordan, Award 31 January 2006, Tokios Tokelės v Ukraine, Award 26 July 2007, Eli Lilly v Canada (UNCITRAL), Final Award 16 March 201),
- Compétence-compétence (Sociedad Anónima Eduardo Vieira v. República de Chile, Award, 21 August 2007),
- res judicata (Amco v Indonesia, Resubmitted Case: Decision on Jurisdiction 10 May 1988, Bosh v Ukraine, Award 25 October 2012, EDF v Argentina, Award 11 June 2012, Apotex v United States (AF), Award 25 August 2014),
- Legitimate expectations (Total S.A. v. Argentine Republic, Decision on liability 27 December 2010),
- prohibition of abuse of right (Phoenix Action v Czech Republic, Award 15 April 2009, Mobil v Venezuela, Decision on Jurisdiction 10 June 2010), and the
- duty to mitigate damage (Mihaly v Sri Lanka, Award 15 March 2002, Vestey v Venezuela, Award 15 April 2016).
E. What to Watch
Looking ahead, several developments will be important for practitioners and academics focused on investment arbitration:
The ILC’s Draft Conclusions do not focus on investment arbitration specifically (although acknowledged in the Special Rapporteur’s reports), but they are highly relevant because they provide a clear taxonomy of GPL, particularly regarding the methods for their identification, clarify their functions, and enhance predictability and coherence.
- Final adoption of the ILC draft conclusions on GPL on second reading, expected at the Commission’s seventy-seventh session (2026), including the revised commentaries.
- How future investment cases will integrate the ILC’s conclusions when dealing with general principles of law.
F. Sources
- International Law Commission: https://legal.un.org/ilc/summaries/1_15.shtml
- First report on general principles of law by Marcelo Vázquez-Bermúdez, Special Rapporteur (A/CN.4/732): https://documents.un.org/doc/undoc/gen/n19/100/93/pdf/n1910093.pdf
- Report on the work of the seventy-fourth session (2023) (A/78/10): https://legal.un.org/ilc/reports/2023/english/chp4.pdf
- Dumberry, P., The Emergence of the Concept of ‘General Principle of International Law’ in Investment Arbitration Case Law (2020).
- Kriebaum U. ´Article 42’. In: Schill SW, Malintoppi L, Reinisch A, Schreuer CH, Sinclair A, eds. Schreuer’s Commentary on the ICSID Convention: A Commentary on the Convention on the Settlement of Investment Disputes between States and Nationals of Other States (2022).