The NEA Integration Group for the Safety Case (IGSC) has served as the most important and effective international platform for developing and integrating the science and engineering necessary to underpin geological disposal. Through its work, the IGSC has demonstrated that deep geological repositories are a safe and effective approach for the disposal of higher activity radioactive wastes and spent nuclear fuel. In its 20th anniversary year, the IGSC reflects on two decades of evolution of the safety case concept through nearly 20 key publications. The main topics addressed by the IGSC are safety assessment methodologies, constructing multiple lines of evidence, organisational and strategic issues, operational and feasibility aspects, regulatory requirements and stakeholder interactions. Together, these topics build confidence in the safety case.