<p>The Ukraine War has thrust the law of neutrality into the spotlight of scholarly debate. This article delves into, through the lens of customary international law, the legal implications of State practice during the Ukraine War for the evolution of the law of neutrality. It argues that none of the unorthodox doctrines proposed to justify military assistance to Ukraine ‒ collective self-defense, qualified neutrality, or optional neutrality ‒ provides a legally tenable basis for such conduct, rendering it a violation of established neutral duties. Crucially, in the absence of accompanying <i>opinio juris</i>, such a violation is insufficient to bring about the desuetude of the existing rules of neutrality, nor do the non-reactions of bystander States to the violation alter this conclusion. At the same time, the practice of a few States may contribute incrementally to the formative process of new customary rules. While the continued validity of the law of neutrality remains largely intact, its efficacy has been markedly undermined by pervasive non-compliance of States providing military assistance to Ukraine. The Ukraine War, potentially shaped by the lawfare strategies of some States, serves as both a catalyst for and the latest manifestation of the ongoing decline in the efficacy of the law of neutrality.</p>