Book excerpt: This book explores the interpersonal world of sibling relationships, explaining how these relationships are central to the development of the psyche of the individual, of the group, of society and of the organisation. Sibling Relations and the Horizontal Axis in Theory and Practice considers four key areas: sibling relations, sibling trauma, the law of the mother and the horizontal axis. The contributors journey through examples from the psychological, philosophical, organisational, social and cultural realms, giving a new perspective on the psychic world and the importance of sibling relationships as an empowering and therapeutic component for building relationships. While we are used to looking at the individual, the group and at society through the vertical, hierarchical relationship that results from parent–child relationships, this book discusses and reveals the impact of the horizontal axis. Sibling Relations and the Horizontal Axis in Theory and Practice will be important reading for psychoanalysts, group analysts and psychoanalytic psychotherapists in practice and in training.