This paper surveys the unprecedented range of justice initiatives mobilized in response to Russia's war of aggression against Ukraine, illustrating how law can be wielded as a strategic instrument of resistance and accountability. It traces the evolution of international, regional, and domestic efforts to document, investigate, and prosecute atrocity crimes, from the activation of existing mechanisms, the ICC, the ICJ, and the European Court of Human Rights, to the design of new institutions such as the Special Tribunal for the Crime of Aggression. Drawing on Ukraine's engagement with these mechanisms and the contributions of its allies, the analysis highlights how the pursuit of justice in Ukraine has advanced the field of atrocity accountability and reinvigorated the post–World War II legal order. The paper also considers the limits of this response, including enduring challenges of enforcement, political will, and selective justice, while underscoring the enduring importance of maintaining a principled commitment to the rule of law amid war.