The sub-field of psychology which focuses on the behavior and mental processes of non-human animals is known as comparative psychology. The two most prominent areas of study under this field are the commonness of behavior across animal species and the relationship of behavior with reproduction. This includes the quantitative and qualitative similarities and differences observed across a wide range of species. The physiological and environmental components which trigger a particular behavior are also studied under this field. It also aims to understand the psychological state of a domesticated or caged species and their corresponding behavior. It also explores typical behavior such as tonic immobility, imitation, hoarding, nest building, etc. This discipline has significant applications in the fields of medicine, ecology and animal training. This book traces the progress of this field and highlights some of its key concepts and applications. While understanding the long-term perspectives of the topics, the book makes an effort in highlighting their impact as a modern tool for the growth of the discipline. It includes contributions of experts and scientists which will provide innovative insights into the field of comparative psychology.