The languages extend through 17 nations in the northern half of Africa: from Algeria to Benin in the west; from Libya to the Democratic Republic of the Congo in the centre; and from Egypt to Tanzania in the east.

As indicated by its hyphenated name, Nilo-Saharan is a family of the African interior, including the greater Nile Basin and the Central Sahara Desert.

Glottolog (2013), for example, a publication of the Max Planck Institute in Germany, does not recognise the unity of the Nilo-Saharan family or even of the Eastern Sudanic branch; Georgiy Starostin (2016) likewise does not accept a relationship between the branches of Nilo-Saharan, though he leaves open the possibility that some of them may prove to be related to each other once the necessary reconstructive work is done.

The distribution of the families may reflect ancient watercourses in a green Sahara during the African humid period before the 4.2-kiloyear event, when the desert was more habitable than it is today.

The Saharan family (which includes Kanuri, Kanembu, the Tebu languages, and Zaghawa) was recognized by Heinrich Barth in 1853, the Nilotic languages by Karl Richard Lepsius in 1880, the various constituent branches of Central Sudanic (but not the connection between them) by Friedrich Müller in 1889, and the Maban family by Maurice Gaudefroy-Demombynes in 1907.

Greenberg's later contribution came in 1963, when he tied Chari–Nile to Songhai, Saharan, Maban, Fur, and Koman-Gumuz and coined the current name Nilo-Saharan for the resulting family.

Roger Blench notes morphological similarities in all putative branches, which leads him to believe that the family is likely to be valid.

[5] Also problematic are the Kuliak languages, which are spoken by hunter-gatherers and appear to retain a non-Nilo-Saharan core; Blench believes they might have been similar to Hadza or Dahalo and shifted incompletely to Nilo-Saharan.

[5] The extinct Meroitic language of ancient Kush has been accepted by linguists such as Rille, Dimmendaal, and Blench as Nilo-Saharan, though others argue for an Afroasiatic affiliation.

Koman (including Gumuz) Saharan Songhay Fur Maban Central Sudanic Kunama Berta Eastern Sudanic (including Kuliak, Nubian and Nilotic) Gumuz was not recognized as distinct from neighbouring Koman; it was separated out (forming "Komuz") by Bender (1989).

His evidence for the classification was not fully published until much later (see Ehret 2001 below), and so it did not attain the same level of acclaim as competing proposals, namely those of Bender and Blench.

Also, unusually, Songhay is well-nested within a core group and coordinate with Maban in a "Western Sahelian" clade, and Kadu is not included in Nilo-Saharan.

Georgiy Starostin (2016),[22] using lexicostatistics based on Swadesh lists, is more inclusive than Glottolog, and in addition finds probable and possible links between the families that will require reconstruction of the proto-languages for confirmation.

In addition to the families listed in Glottolog (previous section), Starostin considers the following to be established: A relationship of Nyima with Nubian, Nara, and Tama (NNT) is considered "highly likely" and close enough that proper comparative work should be able to demonstrate the connection if it's valid, though it would fall outside NNT proper (see Eastern Sudanic languages).

Other units that are "highly likely" to eventually prove to be valid families are: In summary, at this level of certainty, "Nilo-Saharan" constitutes ten distinct and separate language families: Eastern Sudanic, Central Sudanic – Kadu, Maba–Kunama, Komuz, Saharan, Songhai, Kuliak, Fur, Berta, and Shabo.

Gerrit J. Dimmendaal[24][25] suggests the following subclassification of Nilo-Saharan: Maban Kunama Fur Saharan Eastern Sudanic (including Berta) Kuliak Central Sudanic Dimmendaal et al. consider the evidence for the inclusion of Kadu and Songhay too weak to draw any conclusions at present, whereas there is some evidence that Koman and Gumuz belong together and may be Nilo-Saharan.

[26] The large Northeastern division is based on several typological markers: By 2023,[27] Blench had slightly revised the model for a deep primary split between Koman–Gumuz and the rest.

"Core" Nilo-Saharan ("Central African" in Blench 2015) thus appears to be a typological rather than genetic grouping, though Maban is treated as a divergent branch of Eastern Sudanic; Kadu also seems to be quite close.

Saharan and Songhay have some "striking" similarities in their lexicon, which Blench argues is genetic, though the absence of reliable proto-Sarahan and proto-Songhay reconstructions makes evaluation difficult.

In summarizing the literature to date, Hammarström et al. in Glottolog do not accept that the following families are demonstrably related with current research: Proposals for the external relationships of Nilo-Saharan typically center on Niger–Congo: Gregersen (1972) grouped the two together as Kongo–Saharan.

The consonant system reconstructed by Bender for Proto-Nilo-Saharan is: The phonemes /*d₂, *t₂/ correspond to coronal plosives, the phonetic details are difficult to specify, but clearly, they remain distinct from /*d, *t/ and supported by many phonetic correspondences (another author, C. Ehret, reconstructs for the coronal area the sound [d̪], [ḍ] and [t̪], [ṭ] which perhaps are closer to the phonetic detail of /*d₂, *t₂/, see infra) Bender gave a list of about 350 cognates and discussed in depth the grouping and the phonological system proposed by Ch.