In 1917, the October Revolution and the adoption of the revolutionary Mexican Constitution shook the foundations of the international order and international law in profound, unprecedented and lasting ways. The Mexican and Russian revolutions posed fundamental challenges to the still embryonic profession of international law, its practitioners then largely committed to various forms of liberalism and capitalism. In bringing the ‘social question’ to the forefront of international legal debates, the Mexican and Russian revolutions offered new ways of thinking about foundational concepts of property, statehood and non-intervention – and indeed about the very nature of law itself.