The Relationship between Jus Ad Bellum and Jus In Bello

Abstract This chapter discusses the relationship between jus ad bellum (international law regulating the resort to force) and jus in bello (law of armed conflict). It examines state practice, international decisions, and expert opinions to determine how the relationship has been addressed in practice. The chapter considers the question of whether jus in bello applies equally to the unlawful and lawful parties to an armed conflict before turning to the legal implications of the cumulative requirements of the law of self-defence and international humanitarian law (IHL) imposed on a use of force in self-defence. Finally, it considers the legal implications of the concurrent application of Chapter VII of the UN Charter and IHL with respect to use authorized under Chapter VII.