Abstract Globally there is a legacy of radioactive waste associated with more than 50 years of nuclear power generation and weapons production. Typically, this waste is stored at Earth’s surface, and nations are beginning to face up to managing these highly radioactive and hazardous materials for the long term. Nuclear-power generation is increasingly considered as a low carbon, politically secure power source and geological disposal is seen as the favoured route for long-term management of the waste materials produced. Thus, timely implementation of geological disposal is a challenge facing nuclear-power generating societies if we are to demonstrate safe management of these waste materials for the future. In this chapter we review the role that environmental mineralogy has in this critical task. We begin with an introduction to the topic, discuss the waste types and strategies for management, and then discuss the environmental mineralogy of spent fuel and high-level vitrified wastes. We then place the discussion in a geological context with coverage of natural analogue sites, of mineral weathering and stability, and of geochemical conditions that will influence mineral stability. Finally, we discuss mineralogy relevant to the engineered disposal facility as well as the natural environment surrounding the facility in terms of retardation of radionuclide mobility and examine the role of geomicrobiology in nuclearwaste management. Most radioactive waste derives from nuclear power plants as spent fuel. Apart from a few early reactor types, which utilized uranium metal, most reactors use fuel assemblies based on sintered, microcrystalline UO 2 . A small number of reactors are licensed to use a mixed oxide fuel (MOx) based on UO 2 and PuO 2 . In one sense the environmental mineralogy of nuclear waste starts here: what are the properties of these oxides and how will they impact on waste management? Globally, some spent fuel is reprocessed to recover U and Pu for further UO 2 fuel and MOx fuel fabrication. The highly radioactive, fission productbearing acid solutions generated are concentrated, calcined and then incorporated either into glasses as high level waste (HLW) or, perhaps for the future, into various synthetic mineral assemblages ( e.g. ‘SYNROC’ and similar materials). For the spent nuclear fuel that is not destined for reprocessing, packaging in high-integrity metal containers is likely. In addition, operation of the nuclear fuel cycle leads to generation of other intermediate level wastes (ILW) which are most likely grouted and stored in steel drums. ILW and HLW together are categorized as higher-activity wastes and in the UK are destined for geological disposal. The objective of conditioning these wastes (vitrification, packaging or grouting) is to create a much more stable waste form, less likely to release radionuclides into the environment. For HLW, expanding clay minerals are being investigated for use in engineered containment systems, to further delay radionuclide release into the accessible environment by limiting groundwater access. Finally, deep geological disposal concepts take account of geochemical reactions between rock minerals and migrating solute radionuclides to retard their escape in groundwater.