The very nature of international large-scale assessments (ILSAs) raises unique challenges for test developers. The surveys are used across many different countries and translated into multiple languages; they must serve as sound measurement instruments across a very wide range of attainment whilst also engaging students from diverse backgrounds and with very different educational experiences. In order for the surveys to meet the stated aims to evaluate, understand, and improve education worldwide, policymakers must have confidence that the conclusions drawn from the results are relevant and meaningful in their particular jurisdictions. The International Association for the Evaluation of Educational Achievement (IEA) has a comprehensive assessment development process; assessment experts and representatives of participating countries review the material at key points during the test development and throughout strict standards for quality assurance are applied. Care is taken to ensure that consideration is given to diverse perspectives whilst maintaining the integrity and rigor of the assessment instruments as specified in the assessment framework. This established and thorough approach has enabled the assessments to evolve whilst continuing to meet the diverse needs of stakeholders.