Assessment is arguably the most important stage of nursing. It forms the basis for any planned nursing intervention and a baseline against which subsequent events in the hospital stay can be compared. Assessment is an ongoing activity where the patient is continually reviewed and care reappraised to ensure that the patient’s needs are being met. The main aim of this study is to evaluate the reliability and validity of the Byron Physical Assessment Framework (BPAF). The study involved scrutinising the BPAF to describe its purpose, conceptual basis and how it was developed. The BAF was then refined using extensive literature review and expert opinion to improve its comprehensiveness and clarity for its intended purpose. This monograph should be useful to all those attempting to construct and validate clinical assessment and measuring tools. Ruth Harris has the expertise necessary to do this in a sophisticated yet realistic way for practice colleagues.