This guide was developed to help managers and human resource (HR) professionals use assessment practices that are the right choices for reaching their organizations' HR goals. It provides information about assessment practices so that managers and HR professionals can evaluate and select assessment tools and procedures that maximize chances for getting the right fit between jobs and employees; administer and score assessment tools that are the most efficient and effective for their needs; interpret assessment results accurately; and understand the professional and legal standards to be followed when conducting personnel assessment. The guide is structured around a set of 13 assessment principles and their applications. Each of the nine chapters covers one of these critical aspects of the assessment process: (1) personnel assessment; (2) understanding the legal context of assessment--employment laws and regulations with implications for assessment; (3) understanding test quality--concepts of reliability and validity; (4) assessment tools and their uses; (5) how to select tests--standards for evaluating tests; (6) administering assessment instruments; (7) using, scoring, and interpreting assessment instruments; (8) issues and concerns with assessment; and (9) a review of principles of assessment. Two appendixes offer a list of 24 resource materials and a glossary of 44 terms and concepts. (KC)