This Safety Guide defines how to establish a programme and organization for commissioning research reactors. This Safety Guide provides specific recommendations on establishing a programme and organization for commissioning of research reactors to meet the relevant requirements of IAEA Safety Standards Series No. SSR-3, Safety of Research Reactors. It covers the commissioning stages, procedures, reports and documentation and provides guidance for commissioning of new experimental devices and modifications. The recommendations in this publication are intended for use by operating organizations of research reactors, regulatory bodies and other relevant organizations involved in a research reactor project. This Safety Guide is a revision of IAEA Safety Standards Series No. NS-G-4.1, which it supersedes.