“What is and what is defined as populism?” In response to this question the best political theories and philosophies have put forward many different answers, that are taken into account in this article. The article affirms the constitutive ambiguity of the concept of “populism” and its ability to unify very different issues. After analyzing some of the implications that populism entails in practice, the article stresses the link between populism and the end of the logic of the principle of representation, (...) specific of the liberal and democratic theories. The emphasis on the role of the “people” in opposition to the political elites is also a feature of populism, analyzed by the author in this article. In conclusion, the author focuses on the legal field: some of the contemporary constitutional theories, in particular the so-called “popular constitutionalism”, are discussed. These theories, while polemicizing with those authors who overestimate the role of the Supreme Court, reassess the function of the average citizen in the life of constitutional culture, with the intent of favouring greater political participation and strengthening democratic life. (shrink)