This introduction presents an overview of the key concepts discussed in the subsequent chapters of this book. The book takes up ideas about sibling rivalry that may lie at the heart of a particularly intense religious struggle that is engaging the world today. It suggests that it is the relationship between the two half brothers and between them and their father that needs to be explored if we are to understand the conflicts between Judaism, Christianity, and Islam. The book explores the development of democratic ideals from within a psychological theory about the family. It also suggests that sibling relationships have been ignored not only in psychological theories about the family, but also in literary criticism of Western theatre. The book discusses the intricate interweaving of early vertical and horizontal relationships, as they surface in later marital difficulties.