For many years, the impact of sibling relationships on psychological development has been neglected in the literature, overshadowed by the role of the parent-child relationship. As a result, attention to sibling dynamics and sibling transference as valuable information for case formulation and treatment interventions has not been used to its maximum potential. The authors demonstrate how deliberate consideration of sibling dynamics as well as the transferences and countertransferences associated with those dynamics can facilitate treatment. Several important sibling dynamics are discussed, including siblings' influences on identity development; sibling rivalry, jealousy, envy, guilt, and resentment; and sibling attachment. The impact of sibling dynamics on adult love relationships is discussed, as are potential effects of sibling abuse and sibling bereavement. Examples of how these dynamics can manifest themselves in transference and countertransference reactions and suggestions for working with those dynamics are illustrated with clinical examples.