This special issue of Clay Minerals contains 13 full papers presented at the 6th conference on ‘Clays in natural and engineered barriers for radioactive waste confinement’ held in Brussels during 2015. The conference was organized by the Belgian Agency for Radioactive Waste and Enriched Fissile Materials (ONDRAF/NIRAS) together with partner organizations ANDRA (France), COVRA (The Netherlands), NAGRA (Switzerland), NWMO (Canada), POSIVA (Finland) and SKB (Sweden) and a broad international scientific committee. Since 2002, this conference has developed into the most important event for scientists from the world over, dealing with the disposal of highly and long-lived radioactive waste. After...