This chapter reviews the quantifiable impact of social support on PTSD symptom alleviation, emphasizing four support types: emotional/informational support, positive social interaction, affectionate support and tangible support. The response to treatment is best facilitated by positive social interactions and emotional/informational support. Severity of symptoms is reduced by the perception of daily support, with peer support from veterans providing a greater reduction than that from non-veterans. Pre-deployment support does not affect post-deployment PTSD, whereas deployment period support lowers post-deployment PTSD. Prolonged exposure (PE) therapy increases perceived social support, with the effect that there are reductions of intrusions, avoidance and hypervigilance.