Abstract
The chapter will examine whether the law on the use of force—the jus ad bellum—is predicated on the concept of reciprocity. If this were the case, then—simply speaking—a State attacked by another State would be entitled to launch a counter-attack: tit for tat. But is that really the case? In order to ascertain whether this premise indeed holds true, I will first analyse the key structures of the law on the use of force, including in particular the right to self-defence under international law. Having set out the basic contours of the law on the use of force, I will then turn to the fundamental question of whether said rules are based on the principle of reciprocity. Here, the focus will be on the asymmetry between Article (2(4) and Article 51 of the UN Charter and the (potential) ways of coping with this asymmetry. This will be followed by a short conclusion.