Despite the uniqueness and importance of Theropithecus in palaeontological studies, little is known about the geographical and taxonomic differentiation in this genus, now restricted to the Ethiopian Highlands. Traditionally, the single living species Theropithecus gelada (Rüppell 1835) has been considered to comprise two subspecies: the nominate T. g. gelada in the northern highlands, and T. g. obscurus Heuglin 1863, from latitude 12 degrees to 9 degrees N in the south. Both the distributions and the physical characters of these two subspecies are poorly defined, and even in recent major taxonomic revisions, the validity of T. g. obscurus has been questioned. The history of gelada taxonomy and museum collections is reviewed here, and results are compared with the biogeography and major physical features of the Ethiopian Highlands. It is concluded that major gaps exist in our knowledge of the differentiation and distributions of Theropithecus populations. Following this literature review, a series of priority regions for taxonomic research and conservation are identified. These include the gathering of data on (1) geladas inhabiting the Wollo Region, from where obscurus was originally described; (2) the identity of geladas of the Tigray Region northeast of the Tacazzé River, and their current conservation status; (3) the identity of the Shewa population, usually assigned to obscurus; and (4) the identity and current status of geladas found northeast and south of Lake Tana, including Gojjam.