<p>The reactive character of international law is one of its notable features. For the most part, international norms and institutions have been devised&nbsp;in response to&nbsp;<span>previously observed crises and incidents, be they wars, pandemics, environmental disasters, economic breakdowns, or technological advances. The present article challenges this centuries-old reactive and past-oriented approach of international law. It holds that while the reactive paradigm has facilitated adoption of practical solutions to concrete problems faced by the international community, this paradigm has led international law to be backward-looking and short-sighted, hindering the discipline from acting in anticipation of long-term problems and developments.&nbsp;</span></p> <p><span>Against this backdrop, the article calls for a conceptual shift, arguing that it is high time to couple international law’s traditional reactive paradigm with a more proactive, forward-looking approach—one that is geared towards the future with a view to preventing risks and realizing opportunities well in advance. Such a shift, the article contends, is particularly critical given that many of the global challenges on the horizon—such as artificial intelligence, synthetic biology, environmental degradation, demographic transformations, or outer space commercialization—are more complex and diffuse than those encountered in the past. Moreover, these global challenges transpire in an accelerated world, where the rapid pace of social and technological change leaves little room for maneuver when action is due.</span></p> <p>The article begins by recounting the reactive record of international law while illustrating the prevalence of the reactive approach in numerous regulatory fields, including anti-terrorism, public health, refugees, and arms control. Thereafter the article analyzes the root causes of international law’s reactive paradigm and highlights its limitations. The article then turns to lay the theoretical foundations of a novel approach to the evolution and functioning of the discipline, called Proactive International Law. It further presents the proactive approach’s core elements and identifies ways to mainstream them into the international legal system, thereby making long-term (even if uncertain) problems and advancements a real regulatory priority on the international agenda.</p>