This textbook on assessment and outcome measurement is written for both occupational therapy and physiotherapy students and qualified therapists. It begins by defining what is meant by assessment, outcome, evaluation and measurement and discussing the complexity of therapy assessment and measurement, including the challenge of measuring human behaviour and the impact of factors such as task demand and context, including the environment. Methods of data collection (e.g. observation, interview, standardised testing) and sources (e.g. self-report, proxy) for collecting information about clients are then reviewed, and the main purposes of assessment (e.g. descriptive, evaluative, predictive, discriminative) presented. The book then addresses the topics of standardisation, levels of measurement, reliability, validity and clinical utility. There is a chapter describing and applying models for categorizing levels of function to aid assessment and measurement. The concept of clinical reasoning and reflective practice is then explored. Application of principles is supported through detailed case studies and worksheets and the criteria for test critique and guidelines for choosing a particular assessment approach are discussed.