Composition, altitudinal distritbution and syntaxonomy of box communities in the Cadí and Moixeró mountains (Catalan Pyrenees). The floristic composition and some ecological aspects of the Buxus sempervirem woodlands from the Serra de Cadí and Moixeró Mountain (Eastern Pyrenees) are studied. Phytocoenological releves are anaIyzed by classical and by mathematical methodls (FA). Six syntaxa are recognized: Quercetum rotundifoliae buxetosum, Quercetum cocciferae buxo-terebinthetosum, Rhamno saxatilis-Buxetum rubietosum peregrinae, typicum and pinetosum uncinatae, and Buxo-Quercetum pubescentis buxetosum. The first five are integrated in an altitudinal zonation from the calcareous rocky sunny spots, and the last one represents a serial woodland from the montane forests. Rubietosum peregrinae and pinetosum uncinatae are proposed as new subassociations from the Rhamno-Buxetum. The status of suballiance (Amelanchiero-Buxenion) for the alliance Amelanchiero-Buxion O. de Bolòs et Romo 1989 is suggested. The mathematical anaIysis results and the phytocoenological differenciation agree, although transitional forms between some of the studied cornmunities are manifested. Two principal factors of variation are distinguished from the mathematical analysis; one of them is related to the altitude and the other to the mesophylly degree and luminosity.