The use of standardized tests is routinely part of psychological and neuropsychological evaluations. For the data to reflect the constructs of interest (e.g., anxiety, memory), test-takers must respond accurately to background questions, put forth good effort on cognitive tests, and respond in a consistent and honest manner to inventories of psychological functioning. Failure to respond in a valid manner limits the usefulness of the results, except when the purpose of the evaluation is to assess for the presence of deceptive behavior (e.g., malingering). Military personnel may minimize, exaggerate, or fabricate problems for multiple reasons. Therefore, a multi-method approach to assessing the validity of symptoms and performance is an essential component of psychological and neuropsychological evaluations of military personnel, as well as veterans. The purpose of the present chapter is to provide an evidence-based review of validity assessment. Because the availability and use of standardized assessment measures varies within and among countries and cultures, an effort has been made to emphasize principles and procedures that are broadly relevant and therefore more readily useful to practitioners across a range of specific contexts.