Starting from Benedict Anderson’s notion that nationalism evolves around a vernacular readership, this article explores the relation between a nation or ethnic group and ‘its’ language. It analyses the link between ideas about Igbo language and the rise of Igbo ethnic identity in twentieth-century Nigeria. It focuses, first, on how language was introduced as an important marker for ethnic identity, and, second, on how the notion of the existence of an ‘Igbo language’ was successfully employed in debates by Igbo ethnic nationalists and others. Early efforts to standardize the Igbo language were initiated by missionaries and the colonial government, who had also decided upon the boundaries of the Igbo language and the Igbo ethnic group. Most Igbo people preferred literacy in English and were not interested in these efforts. This situation changed after 1940, when the growing influence of the Nigerian anti-colonial movement began to make an impact on the perception of the Igbo language. This does not mean that Igbo became more widely used as a written language. Nearly all articles and pamphlets on the Igbo language and its role continued to be written in English. Also, all attempts to standardize Igbo failed. Thus, the notion of the existence of one shared Igbo language was important and not the existence of a vernacular readership in that language.