An analysis is made of the floristic richness of the Sierra Nevada (southern Spain), where more than 2100 vascular plants were catalogued, thus making it the area with the richest and most varied flora in the western Mediterranean region, including a considerable number of endemic species. In a study of the endangered flora and its protection, 116 taxa are listed as having the most restricted distribution and as being under threat of extinction. Field work for these taxa was undertaken in order to improve knowledge of their habitats, populations, chorology and main threats. Using the new IUCN categories of threat, an analysis was made for each of the taxa, especially those that are critically endangered with a very low number of individuals or very narrow areas of occupancy. Mention is made of the problems posed by the practical application of the new IUCN categories. The main types of environmental impact affecting the flora are also described, including grazing, natural causes, wetland desiccation and water pollution. The highest-lying areas (oro- and cryoro-Mediterranean belts) are where most of the threatened plants are to be found. Since these same plants are mostly endemic to the Sierra Nevada, the need to protect the high peaks of the area is paramount. Reference is made to current legislation protecting threatened plants and the gaps in the European Union Habitats Directive with relevance to the protection of the Sierra Nevada flora. A number of key strategies for protection are proposed.