The history of the study of the terrestrial molluscs of the Eastern Arc Mountains is summarised and a checklist of species known from each range is presented. Current knowledge of the fauna is patchy but each of the ranges contains endemic species and collectively they support a major proportion of the Tanzanian land-snail fauna. Recent research in the East and West Usambara, Uluguru and Nguru Mountains has revealed high levels of mollusc diversity in Bomole and Monga Forests (East Usambara Mountains) and in the limestone forest at Kimboza (Uluguru Mountains); these forests support the richest faunas reported so far from East Africa. In contrast, diversity and abundance is low in the forests of the Nguru Mountains. A similarity analysis is used to identify several clusters of sites that are related to geographical position and altitude. The significance of these findings for the conservation of East African land snails is discussed.