How do people know if they are deceiving themselves? Self-deception is something everyone practices to one degree or another, and it is closely related to other-deception (deceiving other people) and Satan's deception as the father of lies (John 8:44). How dangerous is self-deception? It can cost people their eternal destiny if they are deceiving themselves about their salvation. Self-deception has been a topic of keen interest among philosophers, theologians, and psychologists and is also a significant theme in the Bible. This book first introduces what the fields of philosophy, theology, and psychology say about self-deception and then examines many Bible passages that address the topic of self-deception to gain a biblical understanding of what it is and how to prevent it.