How do international organisations (IOs) balance norms that have conflicting prescriptions? In this article, we build on the literature on norm contestation and norm conflict to identify four ways in which IOs might respond to norm conflicts: (1) consistent norm prioritisation; (2) ad hoc norm prioritisation; (3) balanced norm reconciliation and (4) imbalanced norm reconciliation. How IOs are more likely to respond, we argue, depends on the salience of the norm conflict and the relative strength of the conflicting norms. We illustrate our argument by investigating the norm conflicts that the United Nations (UN) encountered between traditional UN peacekeeping norms and the norm of international criminal accountability in the context of assistance by UN peace operations to the International Criminal Court. Distinguishing between behaviour and discourse as well as headquarters and field levels, we argue that the UN’s response strategies have been largely successful at reducing the tensions generated by the norm conflicts, but that in the longer term they run the risk of both undermining the international criminal accountability norm and damaging the acceptance and credibility of UN peace operations.