Legacy sites are areas contaminated by residual radioactive material deriving from past activities or events that may pose risks to health and safety or the environment, and present technical or administrative challenges to timely remediation. Established in 2010, the International Working Forum on Regulatory Supervision of Legacy Sites (RSLS) aims to promote effective and efficient regulatory supervision of the management of legacy sites, consistent with the IAEA safety standards and good international practices. Intended for use by regulators and operators, this publication presents a summary of activities and outcomes of the first decade of the RSLS with the aim of contributing to a better understanding of the concept of 'legacy sites' and the challenges inherent in their management. It focuses on uranium legacy sites including mines and mills and provides examples of regulatory practices adopted by IAEA Member States. It details key lessons on successful regulatory practices of Member States for managing existing, and preventing future, legacy sites, through the establishment of an efficient national regulatory framework, establishment of clearly defined remediation criteria, requirements necessary to ensure safe remediation, and the importance of and key strategies for engaging stakeholders.