Disasters are a form of collective stress posing an unavoidable threat to people around the world. Disaster losses result from interactions among the natural, social, and built environments, which are becoming increasingly complex. The risk of disaster and people's susceptibility to damage or harm from disasters is represented with the concept of vulnerability. Data from the Indian Ocean tsunami, Hurricane Katrina, and genocide in Darfur, Sudan, show poor people suffer disproportionately from disasters. Disaster social work intervenes in the social and built environments to reduce vulnerability and prevent or reduce long-term social, health, and mental health problems from disasters.