This book gathers a conversation between Luigi Ferrajoli and Juan Ruiz Manero in which three parts can be distinguished. In the first of them, the dialogue runs through the sixties-old cultural atmosphere, the situation of the theory of law in Italy in the sixties / seventies, the teaching exercised by Norberto Bobbio in those same years and the meaning of the democratic magistracy movement. In the second part, which is the central and broadest part of this small volume, there is a confrontation between the models of constitutionalism and, in general, of theory of Law held by each of the authors: between the model «guarantee », Whose main exponent is precisely Ferrajoli, and the model that is usually called« postpositivist »or« principialist », in which Ruiz Manero can be located. The third part of the book is devoted to some salient points of the diagnosis and the therapies proposed by Ferrajoli in reference to some key problems of international relations at present and also, and above all, in relation to what seems an endless Italian constitutional crisis . The set forms an exchange of points of view that shows that the issues dealt with by the theory of Law and the instruments with which they are addressed are of interest to any educated person concerned about the problems of collective life.