This book examines adults’ identifications and internal relationships with their siblings’ mental representations. The authors believe that the best way to illustrate clinical formulations and psychoanalytic theoretical concepts is to provide detailed clinical data. The influence of childhood sibling experiences and associated unconscious fantasies, in their own right, in adults’ personality characteristics, behaviour patterns, and symptoms are presented from seventeen case reports. Clinicians who have patients with fear of pregnancy, claustrophobia, incestuous fantasies, extreme dependency on or murderous rage against siblings, guilt due to the death of a sister or brother in childhood, replacement child syndrome, history of adoption, certain types of animal phobias and related issues will find this volume most helpful. The authors have made a rare, but needed, psychoanalytic contribution that examines mental representations of sisters and brothers in our daily lives.