The concept of ius cogens expresses the tendency to limitate State sovereignty. Looking for the place of ius cogens within positivism demands to deepen the meaning of the terms of reference that affirm its existence. To say that a norm is ius cogens means that it has the necessary force not to be “defeated”. It does not mean that this norm is natural law since it can be modified by other norms of the same character. A norm is “imperative” ex-post facto after a judge has qualified it as such. This does not imply recognizing that the judges would have an unlimited power. On the contrary, the multiplication of international jurisdictions guarantees that no judge has the final word: the content of ius cogens derives from a common denominator found in the international and regional case law, as well as in the case law of national supreme courts.