This chapter analyses the concept of defences in international criminal law. It starts off with some general conceptual remarks defining defences, on a meta level, as exceptions to the (secondary) rule expressed by the respective offence; as such, they do not invalidate this rule—the prohibition sub poena by the offence—but entail its non-application. In the main part, the chapter proposes a systematization along the lines of a substantive/procedural distinction (substantive reasons to exclude individual criminal responsibility versus procedural obstacles/bars to criminal prosecution) and further distinguishing between full and partial defences, justifications and excuses, failure of proof defences, and alibi. On the basis of this classification, a hierarchy of defences is suggested.