Moseley, Christopher. 2007. Encyclopedia of the World's Endangered Languages, 1 edn. Abingdon: Routledge. ISBN 070071197X

Krauss, Michael E. 1979. Na-Dene and Eskimo-Aleut, The Languages of Native America: Historical and Comparative Assessment, 808-901. Austin, TX: University of Texas Press. ISBN 0-292-74624-5

Campbell, Lyle & Marianne Mithun (eds.). 1979. The Languages of Native America: Historical and Comparative Assessment. Austin, TX: University of Texas Press. ISBN 0-292-74624-5

Campbell, Lyle. 1997. American Indian Languages: The Historical Linguistics of Native America, 122. Oxford: Oxford University Press. ISBN 0195094271

Gordon, Raymond G. (ed.). 2005. Ethnologue: Languages of the World, 15 edn. http://www.ethnologue.com/15/web.asp. (09 July, 2008.)

2005. "The World Atlas of Language Structures." edited by Bernard Comrie et al. Oxford University Press.

Bender, M. Lionel. 2000. Comparative Morphology of the Omotic Languages. Munich: Lincom.