It has long been observed that individuals differ one from another on many psychological dimensions. An area of intense interest among psychologists is the measurement of individual differences in personality. Personality is commonly defined as the constellation of traits, or typical and relatively stable patterns of responding to the environment, which are unique to various individuals. An important focus of educational psychology is the assessment of these traits and other related psychological attributes such as interests, preferences, and attitudes. This entry provides a brief overview of the history of personality testing, examines important ethical and psychometric issues related to the use of personality tests in clinical and educational settings, and describes the most commonly administered personality tests.