The totality of admissible rules is an invariant associated to a logic. In my dissertation, I explain how one can describe the admissible rules of a logic and I hint at several ways in which admissible rules provide one with information about a given logic. To be a bit more specific, I describe methods by means of which one can discern between those rules that are and those rules that are not admissible in certain intermediate logics. Moreover, I show that some intermediate logics can be characterised by means of their admissible rules.