This book offers a scientific investigation into the impostor phenomenon, a concept that has long been misunderstood in popular culture.Much of the conventional wisdom about the impostor phenomenon is driven by intuitive, common-sense based recommendations about how to cope with and conquer impostor feelings. Unfortunately, much of this discourse is neither rooted in nor informed by empirical research. There are many important theoretical and methodological questions regarding the impostor phenomenon that remain unanswered, such as whether the impostor phenomenon is a personality trait at the core of one's identity, or merely a predisposition triggered by circumstances or fears of being evaluated.This book describes the theoretical underpinnings of the impostor phenomenon along with common measurement issues, implications for mental health and achievement, its relative prevalence among various population groups, and practical applications of the concept in psychotherapy and mental health treatment more broadly.