This paper presents a survey of the mollusc fauna in Kongsfjorden, an Arctic glacial fjord in Spitsbergen, Svalbard, based on 197 samples collected with van Veen grabs, dredges, scuba-diving collections and baited traps at depths ranging from 5 to 390 m. Eighty-seven mollusc species were recorded. The species distribution accords well with the distribution of the main substrata: barren rock, kelp bed, gravel and soft bottom. For the most common substrate type, the soft bottom, the distribution and diversity of molluscs were analysed in relation to environmental factors. Glacial activity (particularly the inflow of glacial meltwater loaded with mineral solids) is responsible for the main gradients of environmental variables in the fjord. Silt concentration in sediments, the water temperature near the bottom and inorganic suspensions in the surface water best predict the species distribution of the soft bottom. Two faunal associations located in glacial bays and three faunal associations in the central basin of the fjord can be distinguished for the fauna of the soft bottom. Molluscs are much more abundant in glacial bays (200–300 individuals (ind.) 0.1 m2) than in the central basin assemblages (30–40 ind./0.1 m2). Yoldiid (Yoldiella solidula, Y. lenticula and Yoldia hyperborea) and thyasirid bivalves (Thyasira dunbari, T. gouldi and Axinopsida orbiculata) cope particularly well with glacial sedimentation and occur in high quantities in glacial bays. Although there is no effect of glacial disturbance on the molluscan sample species richness and species diversity, there are significant clines of evenness and taxonomic distinctness in areas near to the glacier. The patterns of molluscan diversity are not fully consistent with the patterns described for complete macrobenthic communities.