Founded in 1954, the Spanish Ornithological Society (SEO/BirdLife) is a not-for-profit scientific association whose aims are to conserve wild birds and their habitat throughout Spanish territory, and contribute tothe conservation of biodiversity worldwide by carrying out scientific research; encouraging knowledge of and respect for birdlife and nature in general; and engaging in international development cooperation activities, as a key factor for the conservation and sustainable use of biodiversity in developing countries. Research activities include the creation of the Bird Migration Centre, the organization since 1968 of the National Ornithology Workshop, and publication of the Important Bird Area (IBA) Inventory; an essential input to the design and designation of the state network of IBAs, and perhaps the single most significant contribution of SEO/BirdLife to biodiversity conservation in Spain. In conservation activities, SEO combines a watchdog role with the promotion of environmental awareness in Spanish society. It puts forward plans for bird reserves, advises public agencies on the management of natural spaces, and strives at all times to develop conservation strategies compatible with farming. SEO/BirdLife recently played a vital role, acknowledged by the whole of Spanish society, in the rescue and care of avifauna following two of the gravest ecological disasters in our country’s history: the Doñana toxic spill and the sinking of the oil tanker Prestige. The Important Bird Areas Conservation Programme is one of the pillars of SEO/BirdLife’s conservation strategy, whose aim is to preserve and protect essential birdlife habitats with biodiversity implications. Wild birds are present in every corner of the country, and rank among the most reliable indicators of biological richness and environmental quality. The study of IBAs is therefore a valuable and eminently practical tool for biodiversity conservation. The origin of the Important Bird Areas Conservation Program in Spain is linked to the approval of the EU Wild Birds Conservation Directive, which mandates the creation of a network of Special Protection Areas (SPA) for bird species. The Spanish IBAs programme started a few years later in 1984, and has been and remains a key piece in SEO/BirdLife’s conservation strategy. Its goal is to optimise the conservation status of the best sites for Spain’s most endangered birds through their statutory protection and adequate management, the dissemination of the IBA Inventory, the suspension of all potentially damaging projects and the restoration of degraded habitats. Sustainable development projects have been undertaken in the most significant IBAs, in order to generate benchmarks for compatible management. Also, SEO/BirdLife annually executes some 200-250 conservation actions in selected SPAs. The IBA Inventory has been used by the Spanish government for infrastructure planning and in environmental impact assessments, and by the European Commission as technical support in designating SPAs. The Programme’s credibility and wide take-up among management agencies and government authorities evidences the quality of its contribution to biodiversity conservation, as does the fact that the number and overall extension of Spanish SPAs have doubled in the last five years.