Messies (from mess, English for disorder) are people who drastically limit their living space by, for example, overcrowding their homes with belongings. This book scientifically and clinically describes the phenomenon for the first time. The underlying psychodynamic processes are addressed, as well as group psychoanalysis for Messies and the impact of self-help groups. The goal is to better understand the Messie phenomenon in order to derive consequences for psychotherapeutic work.