Lecture summary: What explains the persistence of the idea of international law’s systematicity in view of its decentralised nature, constantly dependent upon the shifting consent of states and the vagaries of political will? To what extent can its systemic character endure and adapt as the tectonic plates of geo-politics shift? In this lecture, Campbell McLachlan critically re-examines the evidence for the impulse to integrate the disparate elements of international law into a coherent system: the impulse that underpins the principle of systemic integration. He does so in light of the practice of states and international tribunals, which has deepened over the last fifteen years since his research on the principle for the ILC Fragmentation Study Group in 2005. He tests the fruits of this internal analytical perspective against both an increasing scholarly critique and the external disintegrative pressures that the system currently faces––pressures that appear to challenge the very value of global cooperation under law that underpins the idea of systematicity.

Campbell McLachlan KC is Professor of Law at Victoria University of Wellington and 2022–23 Arthur Goodhart Visiting Professor of Legal Science in the University of Cambridge.

He is author of Foreign Relations Law (CUP 2014) and International Investment Arbitration: Substantive Principles (2nd edn, OUP 2017). His book The Principle of Systemic Integration in International Law will be published by OUP in 2023. Elected to the Institut de Droit International in 2015, he served as Rapporteur of its 18th Commission on ‘The equality of the parties before international investment tribunals’, whose resolution was adopted in 2019. He has been invited to give the General Course at The Hague Academy of International Law in 2024. He is an associate member of Essex Court Chambers and Bankside Chambers and currently serves as president of a number of international arbitral tribunals.