Serotonin (5-HT) is a busy neurotransmitter, influencing such varied neuronal processes as memory, mood, emotion, appetite, and even sexuality. A prime role for this neurotransmitter is social behavior, across a variety of species; humans, rodents, primates, and even flies all rely upon serotonin to display normal social behaviors. These social effects are partly mediated through the serotonin receptor 5-HT2CR. This role has been confirmed by pharmacologic treatment, but until recently this work had focused primarily on adult rodents. In this current article, Séjourné and colleagues from the Scripps Research Institute (Florida, USA) for the first time investigated the role of 5-HT2CR in the development of social behavior.