Abstract The general rule on the prohibition on use of force in international relations has rendered controversial the cases in which states may lawfully resort to armed force. Even self-defense, which is undoubtedly a lawful action, is the object of contentious interpretations of its precise content and modalities of exercise. Are there lawful instances of recourse to armed action in addition to self-defense and use of force authorized by the United Nations? This is greatly disputed and the controversy also embodies the legality of intervention for rescuing nationals abroad. The latter's lawfulness is the object of this article, which revisits previous work by the author more than 30 years ago, taking into account new state practice, the scarce jurisprudence, the works of the ILC, the relevant UN declarations and international conventions and the opinions of qualified jurists. The main finding is that the practice of intervention for rescuing nationals abroad, once the prerogative of the Western States, now includes actions by other states belonging to different regional groups. The Russian Federation is the most notable example. This article examines the various circumstances in which the necessity for a rescue operation arises and the justifications that may be invoked. It concludes that intervention for rescuing nationals abroad in mortal danger is allowed by a norm of customary international law, which constitutes an autonomous exception to the prohibition of the use of force in international relations.