This publication developed by the International Nuclear Safety Advisory Group (INSAG) supplements its advice provided in INSAG-10 underscoring application of the principle of defence in depth in nuclear safety for small modular reactors and related emerging technologies. It is intended to stimulate discussion and to promote practical action at all levels to enhance safety of Small Modular Reactors (SMRs). INSAG provides recommendations on current and emerging nuclear safety issues to the IAEA, the nuclear community, and the public. The report is intended for use by governmental authorities and by the nuclear industry and its supporting organizations. In particular, the intended audience includes national decision makers for nuclear power programmes using small modular reactors (SMRs), researchers and designers in this field and nuclear and radiation safety experts.