In the past, collaborations between biologists and psychologists have yielded groundbreaking developments for both fields. This work represents a sophisticated collaboration and integration of knowledge by noted scholars in these fields that holds promise to advance research and understanding of the human-animal bond and the mechanisms of change in animal assisted psychotherapy. The key concepts in this work provide a scientific foundation for understanding why humans and animals develop close bonds, as well as, why animals may have a possible therapeutic effect. The authors utilize a classical ethological framework as an organizational and theoretical platform for their work. An ethological framework proposes that in order to understand behavior, four types of causality should be addressed: What is the potential “adaptive value” in the relationship with regarding reproduction and natural selection? How does this behavior fit with evolutionary history? What is the development of this behavior and what are the physiological and psychological mechanisms allowing for this behavior’s continuation and control? What is the ontological development of the relationship, particularly during early life history? This makes perfect sense in that scientific study of attachment as a neurobehavioral system has origins in ethology. Bowlby (1969, 1973, 1979) borrowed many established constructs from ethology, and the theory of the co-adapted caregiving behavioral system was also founded on ethological principles which was elaborated on and advanced by Judith Solomon who wrote the first forward. A second forward by Sir Patrick Bateson emphasizes the inclusion and importance of oxytocin in the formation of human-animal attachments as “central.” “Such knowledge feeds into the therapeutic uses of animals and their roles in helping humans. These advances form the core of the extremely welcome book” (Bateson, Forward).