Resumen: Four decades of Spain’s NATO membership is enough to devise a balance of this relationship. A balance particularly interesting as, this period has witnessed quite a lot of changes within the international arena; changes that had an impact on our threat perception and on the ways to cope with then. This article analyses the Spanish experiences as Alliance member and different stages of the relationship from two perspectives. The first attends domestic conditions from each side. The second considers the systemic conditions; these ones have dramatically changed since the cold war period. Particular attention deserves the always open to improvement approach to the so-called “South flank”, with an eye on the development of next NATO's new strategic concept. In this regard, the different positions within the Alliance and the demand for treatment analogous to that received by the traditional "East flank" will be addressed. The content of the reflection document for the elaboration of the new NATO strategic concept regarding the southern projection, may imply a change in the nature of the relationship with this area of operations. The research methodology will be based on reflection and doctrinal documents, together with a series of interviews with the support of a previous survey sent to Spanish officers with practical experience in NATO, both in operations and in various managerial positions. Elements of the North American consideration regarding the Spanish participation will also be included. Combined the results with the scientific support of academics, advocacy forums and contributions from think tanks, conclusions and recommendations will be drawn for further and better understanding in the next forty years. Idioma: Español DOI: 10.18847/1.15.5 Año: 2022 Publicado en: Revista de estudios de seguridad internacional 8, 1 (2022), 71-85 ISSN: 2444-6157 Tipo y forma: Artículo (Versión definitiva) Área (Departamento): Área Dcho.Intern.Púb.Relac.In. (Dpto. Derecho Público)