Thesis submitted to the University of Heidelberg and University of Chile in fulfillment of requirements for the academic degree of Master in International Law, Trade, Investments and Arbitration. / On 23rd June, 1947 the Chilean President Gabriel González Videla declared the national sovereignty over the entire continental shelf adjacent to its coast and islands, the soil and subsoil and the superjacent waters to a distance of 200 nautical miles from baselines in order to reserve, protect, preserve and utilize natural resources, giving the starting point of the exclusive economic zone doctrine. Peru and Ecuador, later on, also made statements along the same lines, and, based on these national backgrounds, the three countries signed the Declaration of Santiago on Maritime Zone, on 18th August 1952, by which they proclaimed their sovereignty and exclusive jurisdiction over the sea that bathes the coasts to a minimum distance of 200 nautical miles from the related costs, including soil and subsoil that relate to it in order to prevent irrational exploitation of the natural resources located in it and so important for the development of their peoples. Together with this Declaration, several Agreements were signed and a Regional body was created -The Permanent Commission for the South East Pacific- starting a process of regional cooperation and integration, to which Colombia acceded on 1978, that developed the concept of this new maritime space and spread it around the world. The figure created by these countries was finally recognized in the United Nations Convention on the Law of the Sea adopted on 1982, whose figure of the exclusive economic zone was inspired in the principles and institutions created by the South East Pacific Countries. However, during the Third United Nations Convention on the Law of the Sea, Chile, Colombia, Ecuador and Peru did not share the same view as to the legal nature of the 200 miles zone.. Peru and Ecuador supported a territorial doctrine, which would give an exclusive sovereign position to coastal States over an area of 200 maritime miles, while Chile and Colombia maintained the idea that in this zone, State competences were sovereign but not for all purposes. Even when these different positions never affected the cooperation and friendly relations among these countries, the different approaches with respect to the legal nature of the zone were transferred to the domestic legislation of the States and, until today, can be found in the national legislation of these countries. To us, being the South East Pacific countries the proponents of the 200 miles doctrine, it seems important that they try to maintain harmony in the concept of this maritime zone. Until today, Chile is the only country who had ratified the Convention