Private international law is a field of law that is particularly permeable to its environment. This openness to the outside world has historically manifested itself in the question of the application of foreign law, the answers to which, far from being strictly legal, have also reflected political, economic and geostrategic reasons. Starting from this premise, the course will, firstly, assess the validity of the equation "foreign law = foreign State private law", based on the triple idea of the reformulation of the role of the State at the national and international levels, the acceptance - even encouragement - by the State of the presence of private providers of legal services, and the reappearance of normative realities outside the State, which enjoy varying degrees of acceptance and sympathy. Second, it analyses the usual incoherence between theoretical positions on the nature of applicable law and their practice in most places in the world. This is done, thirdly, overcoming the traditional US-Eurocentric approach to the subject by opening up the study to the responses of a large number of jurisdictions outside the US and Europe, where the future of the discipline will be decided.