The Itsekiri language is a major branch of the Yoruboid group of languages, which as a group, is a key member of the Volta–Niger sub-family of the Niger–Congo family of African languages. Itsekiri is spoken by nearly 900,000 people in Nigeria as a first language and by many others as an additional language notably in the Niger Delta and in parts of Edo and Ondo states of Nigeria. The other key members of the Yoruboid group are Yoruba (22 million) and Igala (1.8 million) along with the various Yoruba dialects spoken in Benin and Togo.
Itsekiri is most closely related to the South Eastern Yoruba dialects with which it shares close similarity in grammar, lexicon and syntax. Itsekiri represents one end of a continuum of Yoruba dialects from the northern Yoruba lands of Oyo and Offa to the western reaches of the Niger-Delta. In many ways standard Yoruba and Itsekiri may be considered official variants of the same language. Although Itsekiri and the South Eastern Yoruba dialects are mutually intelligible to varying degrees depending on proximity to each other, however, unlike Yoruba dialect speakers, native Itsekiri speakers do not recognise or use the standard Yoruba language as their official lingua franca. This may be owing to the historical isolation of the main body of Itsekiri speakers (in the Niger Delta) from the continuum of Yoruba speakers and centuries of developing a separate and distinct Itsekiri socio-cultural and national identity. Nevertheless, from a linguistic standpoint, both Itsekiri and standard Yoruba (based on the Oyo dialect) can be considered to represent two official variants of what is essentially the same language - one is a Southern Yoruba dialectal fusion of Ijebu, Ondo, Owo - spoken as a national language by under a million people and the other a fusion of Oyo and Eko dialects now spoken as a standard language by over 20 million people.
Itsekiri is most closely related to Yoruba and Igala and incorporates elements of both languages. It has also been very heavily influenced by Edo (Bini), Portuguese and English and has taken in loan words from neighbouring Ijo and Urhobo languages.However its basic structure, grammar and vocabulary is essentially Yoruboid with its closest relatives being the south-eastern family of Yoruba dialects - Ijebu, Ilaje-Ikale, Ondo, Akure and Owo. Whilst closely resembling those dialects however the Itsekiri language also features elements of Northern Yoruba notably The Ife and Oyo dialects. It is generally believed that the Itsekiri Language has developed out of an amalgam of languages spoken by various groups present in the western niger-delta at the time of the formation of the Itsekiri nation in the 15th century. Because it has developed in the relative isolation of the Niger-Delta away from the main body of Yoruba dialects and from Igala - Itsekiri like most languages (that develop away from the main family body e.g. Icelandic) has preserved many of the original features of the original proto-Yoruba-Igala language. It is also possible that Itsekiri represents a surviving remnant of what could once have been the original Yoruba-Igala language before the split into separate languages.
Itsekiri is important to philologists and linguists today because of its role in comparative linguistics and in particular the study of the development of the Yoruba language. The Yoruba, English and Pidgin-English languages remain key modern-day influences on the development of the Itsekiri language today.