This paper guides consulting psychologists in how to help managers and group leaders assess group members' reactions, behaviors, and performance. The results may be used for development in improving group performance and for evaluation in making decisions about group members' pay and assignments. Individual and group-level measures of conditions (pressures and opportunities), input, process, and outcomes are considered. The paper discusses who seeks group assessment, the multiple purposes of assessment, models of group process to guide assessment, what is assessed and when, methods for assessment, and who contributes to the assessment process. Implications for inculcating a culture of assessment and continuous learning within groups and organizations.