In what is now Sudan there occurred over the centuries a process of ta'rib, or Arabization, entailing the gradual spread of both Arab identity and the Arabic language among northern peoples. After the Anglo-Egyptian conquest of 1898, British colonial policies favoured a narrow elite from within these ‘Arab’ communities. Members of this elite went on to develop a conception of a self-consciously Sudanese Arabic national identity, in the process adapting the term ‘Sudanese’ (sudani), which derived from an Arabic word for blackness and previously had servile connotations. At decolonization in the 1950s, these nationalists turned ta'rib, into an official policy that sought to propagate Arabic quickly throughout a territory where scores of languages were spoken. This article considers the historical diffusion of Sudanese Arabic-language culture and Arab identity, contrasts this with the post-colonial policy of Arabization, and analyses the relevance of the latter for civil conflicts in Southern Sudan, the Nuba Mountains, and, more recently, Darfur. Far from spreading Arabness, Arabization policy sharpened non-Arab and, in some cases, self-consciously ‘African’ (implying culturally pluralist) identities. Arabization policy also accompanied, in some quarters, the growth of an ideology of Arab cultural and racial supremacy that is now most evident in Darfur.