The South Cushitic or Rift languages of Tanzania belong to the Afro-Asiatic family. The most numerous is Iraqw, with half a million speakers. These languages are believed to have been originally spoken by Southern Cushitic agro-pastoralists from Ethiopia, who in the third millennium BC began migrating southward into the Great Rift Valley.
The Rift languages are named after the Great Rift Valley of Tanzania, where they are found.
Hetzron (1980:70ff) suggested that the Rift languages (South Cushitic) are a part of Lowland East Cushitic. Kießling & Mous (2003) have proposed more specifically that they be linked to a Southern Lowland branch, together with Oromo, Somali, and Yaaku–Dullay. It is possible that the great lexical divergence of Rift from East Cushitic is due to Rift being partially relexified through contact with Khoisan languages, as perhaps evidenced by the unusually high frequency of the ejective affricates /tsʼ/ and /tɬʼ/, which outnumber pulmonary consonants like /p, f, w, ɬ, x/. Kießling & Mous suggest that these ejectives may be remnants of clicks from the source language.
The terms "South Cushitic" and "Rift" are not quite synonymous: The Ma'a and Dahalo languages were once included in South Cushitic, but were not considered Rift. Kießling restricts South Cushitic to West Rift as its only indisputable branch. He states that Dahalo has too many East Cushitic features to belong to South Cushitic, as does Ma'a. (The Waata and Degere may once have spoken languages similar to Dahalo.) Kw'adza and Aasax are in turn insufficiently described to classify as even Cushitic with any certainty.
Iraqw and Gorowa are close enough for basic mutual intelligibility. Alagwa has become similar to Burunge through intense contact, and so had previously been classified as a Southern West Rift language. Aasax and Kw'adza are poorly attested and, like Dahalo, may be the result of language shift from non-Cushitic languages.
Several additional and now extinct South Cushitic languages are deduced from their influence on the Bantu languages that replaced them. A pair of these, Taita Cushitic, appear to have been more divergent than extant Rift languages, co-ordinate with Proto-Rift within a larger group Nurse (1988) calls "Greater Rift".