These areas, particularly the Natural Parks and Reserves, are primarily designed to maintain a balance, in the most harmonious way possible, between the natural environment and the human activities that affect it.

Wetlands such as Paul do Boquilobo and the Tagus Estuary, dune systems such as those at São Jacinto and on the south-west coast, the mountainous regions of Peneda/Gerês, Montesinho, Estrela, Arrábida and São Mamede, coastal cliffs such as those at Sintra/Cascais and on the Costa Vicentina, the scarps of the interior like those along the International Douro, all represent a priceless natural heritage, as well as containing interesting examples of human intervention that make up ecologically and culturally valuable, and sometimes extremely vulnerable, structures.

Meanwhile, Portugal has designated a group of areas, scattered across the country, which are of particular ecological interest within the European context (Nature 2000 network).

However, various areas of the country are already part of international nature conservation networks, such as Biogenetic Reserves (Council of Europe), Ramsar Sites (Ramsar Convention), Biosphere Reserves (MAB/UNESCO) and sites covered by the Convention Concerning the Protection of Wortd Cutturat and Naturat Heritage (UNESCO).