This book provides an in-depth and critical discussion of the positions of three of the most influential thinkers regarding the problem of delusion: Karl Jaspers, Kurt Schneider, and Sigmund Freud, based on the literature. It also systematically presents transcultural psychiatry of delusion and models of aetiopathogenesis. A unique approach attempts to provide a solution to the problem of a clinically consistent definition of delusion, followed by considerations on the significance of the delusional patient's discourse about the "other world." The book offers an initial overview of the complex issues surrounding delusion for those who are not yet familiar with the subject, while also being of interest to professionals due to its largely new perspective. The aim of the book is to help revive the discussion and challenge clinically entrenched schools of thought.