Social media has become a pervasive form of communication, yet little is known about how use relates to stress. Previous research suggests a link between social media use and psychosocial variables such as self-esteem, depression, life satisfaction, and well-being. However, there is limited empirical knowledge concerning how social media use specifically influences and is influenced by stress, with a particular dearth of objective measurement. In a series of studies, this relationship was explored in both laboratory and natural settings. Study I aimed to assess the effect of Facebook use on psychosocial and physiological recovery from an acute social stressor (The Trier Social Stress Test). Participants (n = 92) were randomly assigned to use their own Facebook account or to sit quietly after the stressor. Those who used Facebook experienced prolonged physiological stress when controlling for gender and investment in the website (p < .05). Study II aimed to assess Facebook’s effect on the stress response. Participants (n = 100) were randomly assigned to use their own Facebook account or sit quietly before the Trier Social Stress Test. Those who used Facebook before the acute social stressor experienced lower levels of psychosocial stress, physiological stress, and rated the stressor as less threatening when controlling for gender and emotional investment in the website (p’s <.05). Study III explored Facebook use in the wake of a natural stressor—campus violence. Participants (n = 552) reported using the platform more and in different ways than normal, with importance placed on seeking information, seeking social support, and expressing emotions. Further, users reported that these uses influenced short-term affective state. Together, results highlight the complex relationship between social media use and stress. Users appear to experience stress differently depending on the timing of social media use and stressor onset. Specifically, use after an acute stressor may inhibit stress recovery, while use before may limit stress intensity in the laboratory. Further, use in response to a natural stressor deviates from normal use, and may be beneficial for inducing positive affect. User characteristics and context of use appear to significantly influence the relationship between social media use and stress.