The Pyrenees is a mountain range straddling the border of France and Spain. It extends nearly 500 km (310 mi) from its union with the Cantabrian Mountains to Cap de Creus on the Mediterranean coast. It reaches a maximum altitude of 3,404 metres (11,168 ft) at the peak of Aneto.
For the most part, the main crest forms a divide between Spain and France, with the microstate of Andorra sandwiched in between. Historically, the Crown of Aragon and the Kingdom of Navarre extended on both sides of the mountain range.
A still more marked effect of the preponderance of rainfall in the western half of the chain is seen in the vegetation. The lower mountains in the extreme west are wooded, but the extent of forest declines as one moves eastwards. The eastern Pyrenees are peculiarly wild and barren, all the more since it is in this part of the chain that granitic masses prevail. Also moving from west to east, there is a change in the composition of the flora, with the change becoming most evident as one passes the centre of the mountain chain from which point the Corbières Massif stretch north-eastwards towards the central plateau of France. Though the difference in latitude is only about 1°, in the west the flora resembles that of central Europe while in the east it is distinctly Mediterranean in character. The Pyrenees are nearly as rich in endemic species as the Alps, and among the most remarkable instances of that endemism is the occurrence of the monotypic genus Xatardia (family Apiaceae), which grows only on a high alpine pass between the Val d'Eynes and Catalonia. Other examples include Arenaria montana, Bulbocodium vernum, and Ranunculus glacialis. The genus most abundantly represented in the range is that of the saxifrages, several species of which are endemic here.
In their fauna the Pyrenees present some striking instances of endemism. The Pyrenean desman is found only in some of the streams of the northern slopes of these mountains; the only other desman, the Russian desman, is confined to the Volga river basin in southern Russia, Kazakhstan and Ukraine. The Pyrenean brook salamander (Calotriton asper), an endemic amphibian, also lives in streams and lakes located at high altitudes. Among other peculiarities of Pyrenean fauna are blind insects in the caverns of Ariège, the principal genera of which are Anophthalmus and Adelops.
The Pyrenean ibex, an endemic subspecies of the Iberian ibex, became extinct in January 2000; another subspecies, the western Spanish ibex, was introduced into the area, with the population numbering over 400 individuals as of 2020. The native brown bear population was hunted to near-extinction in the 1990s, but its numbers rebounded in 1996 when three bears were brought from Slovenia. The bear population has bred successfully, and there are now believed to be about 15 brown bears in the central region around Fos, with only four native ones still living in the Aspe Valley.