Relationship science is a major bridge connecting the social, behavioral, and life sciences. It is a deeply theoretical discipline, one characterized by excellent cross-theoretical thinking and research. This inaugural issue of Current Opinion in Psychology showcases some of the newest discoveries in relationship science, discoveries which are beginning to tie together several allied fields. The articles in this special issue are organized around the three major theoretical perspectives that have helped to guide some of the best, most important, and most cutting-edge research currently being conducted in the science of relationships. - interdependence theory, attachment theory, and various evolutionary theories. In this introduction, we offer a brief overview of each theoretical perspective and indicate how each article contributes to the development and/or integration of these theoretical perspectives.