The notion that maternal care and love will determine a child’s emotional well-being and future personality has become ubiquitous. In countless stories and movies we find that the problems of the protagonists—anything from the fear of romantic commitment to serial killing—stem from their troubled relationships with their mothers during childhood. How did we come to hold these views about the determinant power of mother love over an individual’s emotional development? And what does this vision of mother love entail for children and mothers? In The Nature and Nurture of Love, Marga Vicedo examines scientific views about children’s emotional needs and mother love from World War II until the 1970s, paying particular attention to John Bowlby’s ethological theory of attachment behavior. Vicedo tracks the development of Bowlby’s work as well as the interdisciplinary research that he used to support his theory, including Konrad Lorenz’s studies of imprinting in geese, Harry Harlow’s experiments with monkeys, and Mary Ainsworth’s observations of children and mothers in Uganda and the United States. Vicedo’s historical analysis reveals that important psychoanalysts and animal researchers opposed the project of turning emotions into biological instincts. Despite those substantial criticisms, she argues that attachment theory was paramount in turning mother love into a biological need. This shift introduced a new justification for the prescriptive role of biology in human affairs and had profound—and negative—consequences for mothers and for the valuation of mother love.