This chapter argues that, in international legal practice and literature, the actual moment where social reality has engendered a customary norm is never established or traced, but, rather, is always presupposed. According to the argument developed here, the moment custom is made is located neither in time nor in space. Custom is always presupposed to have been made through actors’ behaviours at some given point in the past and in a given place but neither the moment nor the place of such behaviours can be found or traced. In other words, there is never any concrete moment where all practices and opinio juris coalesce into the formation of a rule and which could ever be 'discovered'. This means that the behaviours actually generating the customary rule at stake are out of time and out of space. Because the custom-making moment is out of time and space, it cannot be located, found, or traced, and it must, as a result, be presumed.