According to the common thinking of continental European lawyers, a rule is invalid each and every time either it was not produced in accordance with the metarules which govern the production of rules in the system, or it is inconsistent with a “superior” (higher‐ranked) rule belonging to the same system. Thus, a better understanding of the concept of invalidity demands a careful inquiry into the various kinds of meta‐rules which govern the production of rules as well as into the various (...) kinds of normative hierarchies. The paper is mainly devoted to such an analysis. Five different grounds for invalidity are distinguished. The analysis further shows that invalidity can affect rules as well as legal provisions and legal sources. Further, invalidity should be sharply distinguished from non‐existence (existence being a sufficient condition for rules to be applied). In most legal systems, invalid rules too are susceptible of judicial application: At least, until their invalidity is “declared” (in a constitutive way) by a competent organ (namely, a constitutional court, as far as statutory rules are concerned). (shrink)