A concept for the disposal of intermediate level radioactive wastes involves emplacement within a geological disposal facility, followed by backfilling of the facility with cement. When the closed facility is re-saturated with groundwater, this will create a high pH environment due to dissolution of the cement minerals. Dissolved organic matter (DOM; defined here as naturally occurring organic acids and humin) will be present in the groundwater at a concentration that reflects the host rock environment and the recharge source and pathway. Interactions between DOM and radionuclides may enhance transport away from the facility and are an important consideration in safety performance assessments. This review specifically focuses on studies of DOM–radionuclide interactions at the high pH range that is expected during a repository lifetime. Whilst the vast majority of available data cover binary (DOM–radionuclide) and batch ternary systems (mineral–radionuclide–DOM), this review also covers other potentially important areas, such as reversibility kinetics and redox processes that can be mediated by DOM.