The safe management and disposal of radioactive wastes, from civil and defence nuclear operations, and decommissioning of nuclear facilities, continues to be a challenge of global significance. This MRS symposium, first held in 1978, has emerged as the premier international meeting to address the fundamental and applied science of materials in the context of nuclear waste management. Appropriate to the 40^th anniversary of this symposium, the overarching theme will be retrospectives and perspectives in the state of the art, to address the key question of: how far have we come and where are we going next?

This 40^th symposium will focus on the treatment and disposal of low- and high-level nuclear wastes from commercial power generation, fuel reprocessing, and production of materials for defence. Technologies for interim, short-term, and long-term storage and disposal are of interest, including mature processes as well as new and innovative technologies. Waste form development, including glass, ceramic, metallic, and composite waste forms, will be included, along with methods of processing challenging waste constituents, such as actinides and noble metals. Waste form modelling, performance testing, and advanced characterization techniques will be discussed. Advances in Engineered barrier system (EBS) properties, interactions between engineered and geological systems, radiation effects, chemistry and transport of radionuclides, and long-term predictions of repository performance, will also be discussed.