As might be expected from the difficulty of traversing it, the Sahara Desert has been a fairly effective barrier to direct contact between its two edges; trans-Saharan language contact is limited to the borrowing of non-core vocabulary, minimal from south to north and mostly mediated by education from north to south. Its own inhabitants, however, are necessarily accustomed to travelling desert spaces, and contact between languages within the Sahara has often accordingly had a much greater impact. Several peripheral Arabic varieties of the Sahara retain morphology as well as vocabulary from the languages spoken by their speakers' ancestors, in particular Berber in the southwest and Beja in the southeast; the same is true of at least one Saharan Hausa variety. The Berber languages of the northern Sahara have in turn been deeply affected by centuries of bilingualism in Arabic, borrowing core vocabulary and some aspects of morphology and syntax. The Northern Songhay languages of the central Sahara have been even more profoundly affected by a history of multilingualism and language shift involving Tuareg, Songhay, Arabic, and other Berber languages, much of which remains to be unraveled. These languages have borrowed so extensively that they retain barely a few hundred core words of Songhay vocabulary; those loans have not only introduced new morphology but in some cases replaced old morphology entirely. In the southeast, the spread of Arabic westward from the Nile Valley has created a spectrum of varieties with varying degrees of local influence; the Saharan ones remain almost entirely undescribed. Much work remains to be done throughout the region, not only on identifying and analysing contact effects but even simply on describing the languages its inhabitants speak.