Nilo-Saharan is extremely diverse and thus a somewhat controversial grouping uniting over a hundred languages from southern Egypt to northern Tanzania and into Nigeria and DR Congo, with the Songhay languages along the middle reaches of the Niger River as a geographic outlier. The languages share some unusual morphology, but if they are related, most of the branches must have undergone major restructuring since diverging from their common ancestor. The inclusion of the Songhay languages is questionable, and doubts have been raised over the Koman, Gumuz, and Kadu branches.

Some of the better known Nilo-Saharan languages are Kanuri, Songhay, Nubian, and the widespread Nilotic family, which includes Luo, Dinka, and Maasai. The Nilo-Saharan languages are tonal.