Social support improves psychological and physiological health, and social isolation increases mortality at rates rivaling well-established risk factors such as cigarette smoking, high blood pressure, high blood lipid concentrations, obesity, and lack of physical activity. Although these associations are well established, the mechanisms through which social support exerts its effects remain unclear. This chapter outlines our research on the social regulation of neural threat responding, emphasizing how reliable social support economizes cognitive, affective, and behavioral effort. Specifically, we present social baseline theory, which posits that humans’ default or baseline mode of affect regulation is via social proximity and that the human ecology is acutely social. Indeed, when identifying the dominant human habitat, specific terrestrial features seem unlikely—humans live just about everywhere on earth, subsisting on a great variety of diets and adapting themselves to a diversity of conditions. If humans have created a social ecology—an ecology based on a rich collection of social behaviors and capacities—it follows that other animals could adapt themselves to that ecology. We conjecture that household pets, with a specific emphasis on domesticated dogs, have indeed adapted to the human social ecology and that humans and domesticated pets form veridical social relationships with one another, to great mutual benefit. Companion animals may indeed fulfill the roll of a social support provider—even a relational partner—with consequences for the regulation of neurobiological mechanisms supporting the brain’s threat response and, by extension, for the many consequences of that regulation for health and well-being, both human and animal. In this chapter, we first ground our perception in contemporary theories related to behavioral ecology and perception.