The paper analyses the role of cooperation between States in the contemporary international legal order, with particular attention to the progressive “proceduralisation” of certain obligations. After referencing recent examples of international disputes, the author examines the concept of cooperation in international law, distinguishing it from related notions such as interdependence. The evolution of the principle of cooperation is reconstructed through the United Nations Charter, the Helsinki Final Act, and other legal instruments, highlighting its predominantly procedural nature, based on obligations of information, consultation, and negotiation. The article also emphasises the connection with the principles of good faith and due diligence, showing how in various international regimes – from environmental protection to trade and even the global commons – substantive rules are increasingly being replaced or complemented by procedural obligations. This trend toward “proceduralisation”, also present in the legal system of the European Union, contributes to strengthening interstate cooperation through verifiable and shared mechanisms.