The work analyses the international law rules governing the exercise of jurisdiction of the port state on foreign vessels. The basis of such jurisdiction is traced in international customary law as emerging by states praxis and the application of such rule is analysed by examining the relevant international instruments which contemplate the possibility to exercise such jurisdicton. specific analysis is made of the contribution of the International Maritime Organisation in developing a state common approach to port state jurisdiction and the impact of such approach on the sector of maritime safety.