Siblings are often associated with the idea of deep connection, but also with rivalry. They are ubiquitous in mythology and fairy tales, biographies, novels, and films. In striking contrast to daily life experiences and cultural significance, sibling relationships were nearly completely overlooked in psychoanalytic discourse until the 1980s or reduced to a negative potential. In response to this gap, Hans Sohni presents a psychoanalytic developmental psychology of vibrant sibling relationships, incorporating family theoretical, developmental, and preventive approaches. He considers the sibling status as a distinct life experience, highlights its influence on personality development, and examines the dynamics of differentiation and relatedness. Sohni demonstrates the possibilities that arise from considering this topic.