As Nordic states and their allies embark on ever more challenging military operations abroad, the complexity of the applicable rules – and legal consequences they may have – is growing rapidly. In addition to the specific terms of the mandate and the underlying principles of the UN Charter, there are two regimes that govern the conduct of military and other security forces across the war-peace spectrum: the law of armed conflict (LOAC) and international human rights law (IHRL). The exact application of these regimes and their interaction remain matters of debate. Yet, the most vexing question is: what happens when it is not one state’s own forces, but those of a partner that run afoul the LOAC and IHRL standards? This article maps and disentangles the relevant international rules and regimes under which responsibility may arise for states due to abuse committed by their partners in military operations abroad. It considers the general rules of state responsibility – in particular, the rule on state complicity – and the relevant substantive rules under the LOAC and IHRL as well as the Arms Trade Treaty and the UN Human Rights Due Diligence Policy. By and large, states have to abstain from any form of assistance that could contribute to the commission of IHRL and LOAC violations by their partners. Under certain circumstances, they even have to actively and continuously assess the risk of such misconduct occurring and take mitigating measures. Nevertheless, these obligations do not not necessarily translate into an effective system of accountability.