In conducting psychological assessments to identify psychopathology, it is essential that clinicians continue to engage in activities that help them remain current on the state of the science. The models to conceptualize psychopathology, the diagnostic criteria, and the instruments used to inform clinicians in arriving at diagnoses and treatment plans continue to evolve. The assessment of psychopathology is rooted in knowledge of the empirical evidence of the diagnostic criteria, and a lack of current information of the empirical evidence can lead to faulty application of assessments or incorrect conclusions regarding diagnoses. Interviews, behavioral observations, self-report inventories, psychological testing, historical/medical record review, functional assessment, and clinical judgment are all necessary in the formation of a diagnostic picture that provides an accurate depiction of clients’ current issues and the selection of interventions that are likely to be the most effective.