Introducing a special issue of Sociologia del diritto devoted to the lex mercatoria, the author starts with an outline description of the state of the art of knowledge about the phenomenon, drawn from the literature at high theoretical levels related closely with those of globalisation and the crisis of the modern state. He then underlines the lack of any sufficient apparatus of empirical knowledge in the sociology of law about concrete applications of the lex mercatoria. A more detailed examination of the phenomenon could enable not only several important middle-range problems to be solved, but, by revealing the many bonds that link this type of contract law to national and international (e.g. European) legislation, might also prepare the way for certain commonplace assumptions, such as the crisis of state law of a political origin and of the state itself, to be questioned anew.