This Safety Guide considers the application of a graded approach throughout the lifetime of a research reactor (site evaluation, design, construction, commissioning, operation and preparation for decommissioning), including utilization and experiments that are specific features of research reactor operation. A major aspect of this Safety Guide involves the use of a graded approach in the application of the safety requirements for the design and operation of research reactors, so that the fundamental safety objective to protect people and the environment from harmful effects of ionizing radiation is achieved. It is intended for use by operating organizations, regulatory bodies and other organizations involved in the design, construction and operation of research reactors. This Safety Guide is a revision of IAEA Safety Standards Series No. SSG-22, which it supersedes.