Lying is a part of normal psychological behavior; it can be triggered by feelings of shame or guilt, and is often used to avoid conflict. However, pseudologia fantastica is characterized by the creation of eloquent and interesting stories, sometimes bordering on the fantastic, that are told to impress others. These stories may seem to be just on the verge of believability and often involve the patient assuming important and heroic roles. Patients react to questions or doubts with ad hoc elaborations in order to satisfy the listener. Thus, new lies are needed to supplement the old, and patients sometimes start to believe their own deceptions. Detection of pathological lying and differential diagnosis are, not surprisingly, quite difficult, and require modifications to standard assessment procedures. The chapter also discusses the known associations of pseudologia phantastica with other psychiatric conditions.