Even twins are unique. Most people idealize twins, fantasizing a close, perpetually loving relationship. Yet Klein, herself an identical twin, demonstrates that twins have complicated and intense relationships that range from over-identification or excessive closeness to profound estrangement and conflict. Most twins who are raised as individuals deal with the significant emotional pain of separation in adolescence or young adulthood, yet as mature adults can come to love and respect each other as individuals. As Klein makes clear, the parenting that twins receive as infants and young children affects the relationships that they have with one another and with the world they choose to function in. Because parenting is a critical determinant of psychological well-being, it should be treated as a serious but manageable challenge.