Validity is a clear, substantive introduction to the two most fundamental aspects of defensible testing practice: understanding test score meaning and justifying test score use. Driven by evidence-based and consensus-grounded measurement theory, principles, and terminology, this book addresses the most common questions of applied validation, the quality of test information, and the usefulness of test results. Concise yet comprehensive, this volume’s integrated framework is ideal for graduate courses on assessment, testing, psychometrics, and research methods as well as for credentialing organizations, licensure and certification entities, education agencies, and test publishers.