Psychologists evaluating patients who may have psychological or neuropsychological impairment integrate data from clinical interviews, record reviews, and other sources to determine the presence and degree of impairment. An essential part of this process is assessing whether the patient is providing an accurate representation of their psychological or cognitive status on selfreport or neuropsychological measures. This book explores the conceptual underpinnings and empirical studies supporting the use of symptom and performance validity measures in psychological assessment. It provides a practical framework for integrating validity test results with other clinical data, helping clinicians distinguish between nonintentional forms of disability exaggeration (e.g., somatization) from intentional overreporting (e.g., malingering). Designed for psychologists, neuropsychologists, and trainees, this book offers practical guidance for incorporating validity assessment into routine practice and to interpret assessment data with confidence and scientific rigor.