One of the most controversial rules of private international law is the exception of public order, the rule not to enforce foreign laws which are contrary to the fundamental conceptions of the law of the state having jurisdiction. There is no country in which this exception has not played an important rôle in the refusal to enforce foreign laws, and numerous writers have discussed the importance and difficulties of the exception of public order. Its problems had been thoroughly studied before the World War by many authorities on private international law, among others by Bustamante, Fiore, Kahn, Klein and Pillet, without a uniform solution having been reached. When, after the war, the states began to reestablish their international relations, the exception of public order began anew to play its rôle in the courts the world over, and to put the same difficulties before the judges dealing with cases of conflict between domestic and foreign laws.