This book presents a thorough investigation of Griesinger, Kahlbaum, and Kraepelin’s foundational works in psychiatry. It offers an admirable opportunity to understand their achievements and thoughts, and its historical character makes it accessible to a wide range of readers interested in mental health. The analysis of continuities and discontinuities in their described mental disorders illuminates the current classification and diagnosis debate in psychiatry. This analysis comprises etiologic explanations and methodological grounds for each author’s classification. Implying an interrelation among the disorders, the unitary psychosis allows or demands a comprehensive mental disorder view, which includes the person. In this respect, other psychopathologists are also investigated in this book, and process philosophy is introduced, suggesting a fertile framework for psychopathology. According to German Berrios in his Preface, the book offers a new perspective on the nature and meaning of the concept of unitary psychosis.