Maritime zones under national sovereignty or jurisdiction, as defined in the United Nations Convention on the Law of the Sea (UNCLOS), include inland maritime waters, the territorial sea, the exclusive economic zone, including the area adjacent to the territorial sea, and the continental shelf. Portugal has defined its maritime zones, whose limits have been established in Law No. 34/2006 of 28th July.

As a whole, the so-called national maritime space covers about 4 million km2 of sea areas, giving Portugal the status of the largest EU coastal State and also one of the largest in the world. Duties of Coastal States in Marine Zones under Sovereignty or Jurisdiction:  UNCLOS, while establishing the rights of coastal States on the exploitation of natural marine resources, also establishes the environmental duties these States must respect in their exercise.

Thus, coastal States have a duty to adopt measures for the prevention, reduction and control of pollution and cannot transfer pollution to other marine zones. They also have a duty to protect vulnerable marine ecosystems, endangered marine habitats, endangered marine species and other forms of marine life, and prevent the accidental or intentional introduction of alien species.