Personality can be defined as “the unique way in which each individual thinks, acts, and feels throughout life” (Ciccarelli, 2015). From the earliest perspectives of Greek and Roman philosophers, to the construction of psychodynamic, behavioral, humanistic, social cognitive, trait, and biopsychosocial theories, these paradigms attempt to explain the essence of our being. We’ll examine the theoretical models and discuss how the influence of family, friends, and major life events help to shape our personality. We will also review the more commonly used personality tests and conduct an individual personality assessment. Lastly, we will explore the symptoms and criteria used by psychologists and psychiatrists to diagnose personality disorders and their impact on interpersonal relationships.