The concept and establishment of Ecological Networks (EN) have been seen as a solution towards nature conservation strategies targeting biodiversity and ecological connectivity. Within this, the EN assumed a holistic view of land-use planning and biodiversity conservation as the core of the wider Green Infrastructure (GI) framework. The EN is considered a spatial concept recognized as a system of landscape structures or ecosystems, and a strategically connected fundamental infrastructure of abiotic and biotic systems, underlying the provision of multiple functions valuable to society. This concept moves beyond traditional approaches of “nature protection and preservation”, (re)focusing on the ecosystemic approach and the “continuum naturale”, emphasising the quality or potentiality of physical components, allowing the articulation with the nature conservation and at-risk areas. Portugal has long had legislation in place meant to protect the natural resources. Although the environmental policies are sectoral and unarticulated, and the environmental data is dispersed and absent. In addition, this study shows that the existing protected areas in Portugal, namely Natura 2000 and classified protected areas, are insufficient to ensure landscape ecological balance and avoid fragmentation. The main goal is to develop a methodology to map a National Ecological Network (NEN) for mainland Portugal, establish the theoretical framework of the EN/GI, by identifying and mapping the most valuable and sensitive areas that guarantee the ecosystem functioning through a multi-level ecological evaluation criteria that integrate the physical and biological systems. The Portuguese NEN map, with a 25 m spatial resolution, integrates in a single tool the Portuguese environmental policies more effectively, in order to facilitate its understanding and application into planning. Regarding the EN mapping method, it was used a GIS-based model made up of a sequence of analyses and evaluations that are driven by a GIS supported assessment of several indices/models used for each EN component. These NEN components were studied individually and collectively and the results, hierarchized in two levels, show that most of the ecological components do not overlap. The NEN1 has high biodiversity and ecological value, which means they are more vulnerable to anthropogenic activity. NEN1 covers a total of 67 % of the mainland, yet as of 2018, only 25 % is protected in nature conservation areas. Priority of action must be given to NEN1 in order to avoid/decrease landscape fragmentation, environmental risks, and natural disaster prevention. This paper contributes to the understanding of the NEN importance as an ecologically based tool towards a more sustainable landscape planning, and the basis of the development plans at national, regional and local levels in an integrated manner, instead of a compilation of disassociated often-contradictory planning tools. The benefits of a Portuguese NEN into a GI development and part of a (broader) nature base solutions by increasing the ecosystems quality and become less dependent on economic and social activities, helping in the restoration of degraded ecosystems and environmental risk prevention. Moreover, it represents the first attempt to map Portuguese EN, and addresses the lack of mapping and the inconsistent EN criteria. It is available online at http://epic-webgis-portugal.isa.ulisboa.pt.