Some classifications split the colobine monkeys into two tribes, while others split them into three groups. Both classifications put the three African genera Colobus, Piliocolobus, and Procolobus in one group; these genera are distinct because they have stub thumbs (Greek κολοβός kolobós = "docked").
The various Asian genera are placed into one or two groups. Analysis of mtDNA shows the Asian species form two distinct groups, one of langurs and the other of the "odd-nosed" species. The grey langurs are not closely related to either.
- Groves, Colin; Wilson D.E. & Reeder D.M. (eds) 2005. Mammal species of the world. 3rd ed, Johns Hopkins University Press, pp. 152-178. ISBN 0-801-88221-4
- Sterner, Kirstin N. et al 2006. Mitochondrial data support an odd-nosed colobine clade. Molecular Phylogenetics and Evolution 40 (1): 1–7. PMID 16500120.