The system of international trade is usually taken as a set of rules which has remained practically fixed since the first years following the second World War. It is considered as the legal framework which greatly facilitated the international exchange of goods and services during the last 25 years. Changes - like the conclusion or termination of agreements between states or the putting in and out of operation of national laws and regulations - normally left the system intact because they occurred within the framework of these rules. If they collided with them they were either regarded as temporary deviations or as concessions (exceptions) which were unavoidable, mostly for political reasons. It is, however, doubtful if this conception is still correct, since the deviations and exception have now reached dimensions which can no longer be called negligible. Moreover, these deviations and exceptions are scarcely temporary at all. This can be demonstrated with regard to the three basic principles of the system of international trade: Reciprocity, Most-favoured nation treatment and Liberalization.