The South Cushitic or Rift languages of Tanzania are a branch of the Cushitic languages. The most numerous is Iraqw, with half a million speakers. Scholars believe that these languages were spoken by Southern Cushitic agro-pastoralists from Ethiopia, who began migrating southward into the Great Rift Valley in the third millennium BC.
The original homeland of Proto-South Cushitic was in Southwest Ethiopia. South Cushitic speakers then migrated south to lake Turkana and further south, entering Tanzania in 2000BC.
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 influenced 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.) He deems Kw'adza and Aasax 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, maybe the result 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. Two of these, Taita Cushitic, appear to have been more distinct from the current Rift languages than other related languages. They are similar to an earlier form of Rift, which Nurse (1988) calls "Greater Rift".