Social interactions are essential for animals to survive, reproduce, raise their young. Over the years, my lab has attempted to decipher the unique characteristics of social recognition: what are the unique cues that trigger distinct social behaviors, what is the nature and identity of social behavior circuits, how is the function of these circuits different in males and females and how are they modulated by the animal physiological status? In this lecture, I will describe our recent work uncovering how discrete, molecularly defined neuronal populations participate in the positive and negative control of the drive for social interactions when animals are isolated or part of a group, and share our new insights into the brain-wide response to social isolation. Finally, social behavior is highly affected in sick animals and I will describe our recent progress in understanding how specific brain circuits and cell types direct adaptive changes in behavior during various forms of sickness in mice, providing a new framework to understand the function and modulation of behavior circuits in health and disease.