This TECDOC, developed through the Regulatory Track of the Nuclear Harmonization and Standardization Initiative (NHSI), presents a framework to enhance information-sharing and cooperation among regulatory bodies. It aims to improve cooperation during regulatory reviews of advanced reactor designs, with particular emphasis on small modular reactors (SMRs). Drawing on insights from multinational review activities and ongoing international harmonization efforts, the document serves as a guide for regulatory authorities, technical support organizations, and industry stakeholders involved in the licensing of advanced reactors. By fostering cooperation and alignment of regulatory practices, this TECDOC helps reduce design modifications driven by national regulatory differences, thereby improving the efficiency of global regulatory reviews. Ultimately, the regulatory cooperation and adoption of harmonized approaches support the safe and efficient deployment of advanced reactors.