The neuropeptide oxytocin plays a critical role regulating social cognition and behavior in animals, and recent work manipulating the availability of oxytocin indicates parallel effects in humans. To date, however, studies have been somewhat inconsistent with some showing “prosocial” effects, but others showing null, or even detrimental social effects. We review the literature on the social effects of oxytocin in humans, specifically highlighting this context- and person-dependent variability. Adopting an interactionist perspective, we argue that this variability is meaningful and may shed light on the underlying mechanism(s) by which oxytocin modulates human sociality. We also consider work measuring peripheral oxytocin and oxytocin-related genes, and discus whether the person-dependent effects may relate to the endogenous oxytocin system.