The Ijo languages are traditionally considered a distinct branch of the Niger–Congo family (perhaps along with Defaka in a group called Ijoid). They are notable for their subject–object–verb basic word order, which is otherwise an unusual feature in Niger–Congo, shared only by such distant potential branches as Mande and Dogon. Like Mande and Dogon, Ijoid lacks even traces of the noun class system considered characteristic of Niger–Congo. This motivated Joseph Greenberg, in his initial classification of Niger–Congo, to describe them as having split early from that family. However, owing to the lack of these features, Linguist Gerrit Dimmendaal doubts their inclusion in Niger–Congo altogether and considers the Ijoid languages to be an independent family.
The following internal classification is based on Jenewari (1989) and Williamson & Blench (2000).
In June 2013, the Izon Fie instructional book and audio CDs were launched at a ceremony attended by officials of the government of Bayelsa State. The Niger Delta University is working to expand the range of books available in the Ijo language. Translations of poetry and the Call of the River Nun by Gabriel Okara are underway.
Williamson, Kay. 1973. Some reduced vowel harmony systems. Research Notes 6:1-3. 145-169.
Williamson, Kay. 1977. Multivalued features for consonants. Language 53.843-871.
Williamson, Kay. 1978. From tone to pitch-accent: the case of Ịjọ. Kiabàrà 1:2.116-125.
Williamson, Kay. 1979. Consonant distribution in Ịjọ. In: Linguistic and literary studies presented to Archibald Hill, ed. E.C. Polome and W. Winter, 3.341-353. Lisse, Netherlands: Peter de Ridder Press.
Williamson, Kay. 1979. Medial consonants in Proto-Ịjọ. Journal of African Languages and Linguistics 1.73-94.
Williamson, Kay. 1987. Nasality in Ịjọ. In: Current trends in African linguistics, 4, ed. by David Odden, 397-415.
Williamson, Kay. 1989. Tone and accent in Ịjọ. In Pitch accent systems, ed. by Harry v.d. Hulst and Norval Smith, 253-278. Foris Publications.
Williamson, Kay. 2004. The language situation in the Niger Delta. Chapter 2 in: The development of Ịzọn language, edited by Martha L. Akpana, 9-13.
Williamson, Kay, and A. O. Timitimi. 1970. A note on number symbolism in Ịjọ. African Notes (Ibadan) 5:3. 9-16.
Williamson, Kay & Timitime, A.O. (197?) 'A note on Ijo number symbolism', African Notes, 5, 3, 9-16.
Filatei, Akpodigha. 2006. The Ijaw Language Project. (Editor of www.ijawdictionary.com). www.ijawdictionary.com
On specific languages
Williamson, Kay. 1962. (Republished by Bobbs-Merrill Reprints 1971.). Changes in the marriage system of the Okrika Ịjọ. Africa 32.53-60.
Orupabo, G. J., and Kay Williamson. 1980. Okrika. In West African language data sheets, Volume II, edited by M.E. Kropp Dakubu. Leiden: West African Linguistic Society and African Studies Centre.