IAEA Member States have expressed relevant interest in the development and deployment of small and medium-sized or modular reactors (SMRs) to help cover their energy needs in the coming decades. SMR designs may include technological characteristics that differ significantly from those of the large nuclear power plants that are commercially available. Those SMR characteristics can represent a challenge when the existing design requirements, as established in IAEA Safety Standards Series No. SSR-2/1 (Rev. 1) Safety of Nuclear Power Plants: Design, are intended to be applied to SMRs. This publication focuses on the engineering judgement necessary to apply each of the design requirements in SSR-2/1 (Rev. 1), and also the entire set of requirements, to light water cooled and high temperature gas cooled SMRs. The publication includes the common ground reached by representatives from regulatory bodies, technical and scientific support organizations (TSOs) and SMR design organizations regarding the applicability of the design requirements to both SMR technologies. The insights provided are also intended to contribute to motivating further progress in the harmonization of national and international views on safety approaches for SMR technologies. This publication is intended for use by organizations dealing with nuclear power plant design or operation, and by regulatory bodies and TSOs, particularly from countries that are initiating or enlarging nuclear power programmes that include SMR units.