This authoritative guide directs consumers and users of test scores on when and how to provide subscores and how to make informed decisions based on them. The book is designed to be accessible to practitioners and score users with varying levels of technical expertise, from executives of testing organizations and students who take tests to graduate students in educational measurement, psychometricians, and test developers. The theoretical background required to evaluate subscores and improve them are provided alongside examples of tests with subscores to illustrate their use and misuse. The first chapter covers the history of tests, subtests, scores, and subscores. Later chapters go into subscore reporting, evaluating and improving the quality of subscores, and alternatives to subscores when they are not appropriate. This thorough introduction to the existing research and best practices will be useful to graduate students, researchers, and practitioners.