Defeasible inheritance networks are a non-monotonic framework dealing with hierarchical knowledge. On the other hand, rational closure, a main representative of the preferential approach, is acknowledged as a landmark. We will combine these two approaches and define a new non-monotonic closure operation for propositional knowledge bases that combines the advantages of both. Then we redefine such a procedure for Description Logics, a family of logics well-suited to model structured information. In both cases we will provide a simple reasoning method that is build on top of the classical entailment relation.