The Byrranga Mountains (Gory Byrranga) are the most northern mountainous massif of the Taymyr Peninsula (Poluostrov Taymyr) in the Russian Arctic. Although studies of them began in 1736, they are one of the least studied areas of the Arctic. The region has no population, is remote, and has difficult access. As a result, the mountainous tundra ecosystems are preserved practically in a pristine state. The mountains are composed of siltstones and intrusive rocks of neutral composition; vast areas along all the mountain chain are occupied by exposed limestone. Rivers flow in deep intermontane depressions while lakes are found mainly in faults. The climate is an extremely severe continental type. Microclimatic areas provide some relief and support a rich and diverse flora. There have been 391 species and subspecies of vascular plants recorded, but no reliable data on the number of species of mosses and lichens are available. Relict thickets of tall willows are found in protected valleys of piedmont brooks, whereas relict alder-tree thickets occur on warm slopes. The mountain fauna includes nine mammal and 56 bird species. Intermontane depressions serve as corridors for seasonal migrations of wild reindeer that usually spend summers in the southern piedmont areas. Northern piedmonts and wide intermontane depressions are places where herds of musk-ox, introduced in the 1970s, concentrate. The bird fauna of relict willow thickets is highly specific and the fish fauna is quite diverse (16 species), but some species in Taymyr Lake (Ozero Taymyr) have been overexploited. This paper provides the first detailed biogeographical description of the Byrranga Mountains in English.