The book fills the gap in psychological and psychoanalytic literature regarding the influence of horizontal connections in the family (within one generation) on the formation of personality and the development of psychopathological features in children and adults. It is emphasized that the appearance of a new child in the family is acutely experienced by his closest brothers and sisters, changes the family structure and the emotional ties that have developed in it. Under-discussed and silent issues of sibling life are addressed: violence, sibling sexual relations, fulfillment of prohibitions and taboos, sexual aspects of attachment - and more general issues: gender-gender balance, the relationship of oedipal and sibling relationships, historical, ethnic and social factors in sibling life.