This publication presents "IEA's Technical Standards for International Large-Scale Assessment." The initial standards, published in 1999, aimed to consolidate the best practices and methodological rigor in IEA's approach to educational assessment, addressing the unique needs of international studies. The standards presented in this publication reflect IEA's ongoing commitment to maintaining the highest levels of quality in IEA's studies and contributions to the field of international large-scale assessment (ILSA). Since 1999, many changes have taken place in the field of ILSA, including in IEA studies. The 2025 standards were built on the foundations of the 1999 standards and have been revised and expanded to accommodate these changes. The four flagship IEA studies--TIMSS, PIRLS, ICCS, and ICILS--are computer-based and cyclical, which offers new opportunities but also new challenges. In addition, since 1999, processes, techniques, and methodological approaches have evolved and contributed to all aspects of study design, operationalization, implementation, analysis, and reporting. The evolution of ILSA, including IEA studies, has necessitated revision of existing standards and, in some cases, the development of new standards to guide their design and implementation. The 2025 standards have been published as a resource to support the many stakeholders in international research, from those directly involved in study implementation to those seeking to use ILSA data and evaluate and refine ILSA as part of a process of continuous improvement.