This paper considers multiple meanings of the expression ‘dual use’ and examines lessons to be learned from the life sciences when considering ethical and policy issues associated with the dual-use nature of nanotechnology (and converging technologies). After examining recent controversial dual-use experiments in the life sciences, it considers the potential roles and limitations of science codes of conduct for addressing concerns associated with dual-use science and technology. It concludes that, rather than being essentially associated with voluntary self-governance of the scientific community, codes of conduct should arguably be part of a broader regulatory oversight system.