Sibling relationships ar a new field in empirical science, and existing data are rather sparse. An overview will be given about the diversity of sibling relationships. General research results will be reported briefly, and special emphasis will be put on the situation of siblings in families undergoing divorce. Starting with the situation of current research an their diverse results two major studies will be described more closely (Conger and Conger 1996; Schmidt-Denter and Beelmann 1995). Furthermore problems of research in the area of sibling relationships will be discussed. Implications of these research results for expert opinions in custody cases will be presented (Karle et al. 2000). A following case study will again demonstrate the complexity of this topic.