This report summarises the lessons to be drawn from the three-year collaborative social sciences research project ‘International Socio-Technical Challenges for implementing geological disposal’ (InSOTEC). Adopting an approach that is relatively novel in this context, the project focused its investigations on the complex interplay between what are typically seen as distinct technical and social dimensions of radioactive waste management (RWM), in particular in the context of the design and implementation of geological disposal. The aim of the InSOTEC project was not to arrive at a prescription for facilitating the implementation of geological disposal, but to foster and deepen the growing awareness of the interaction between social and technical aspects of RWM that has been evident within the technical expert community by providing stakeholders and experts of all kinds with a better understanding of the processes that shape the challenges which confront them. The report brings together insights for RWM that have been generated within the different research strands of the project and offers observations on their implications for practice, addressing in particular the processes of research and development, public and stakeholder involvement in RWM, and long-term governance of geological disposal of higher activity radioactive wastes