Although most victims of disasters, terrorism, or other shocking events recover on their own, a sizable amount of these victims develops long-term disaster-related problems. These victims should receive timely and appropriate psychosocial help. This article describes the development of guidelines on psychosocial interventions during the first 6 weeks after a major incident. Scientific literature, expert opinions, and consensus among relevant parties in the clinical field were used to formulate the recommendations. Early screening, a supportive context, early preventive and curative psychosocial interventions, and the organization of interventions are covered. The implications for the clinical field and future research are discussed. It is concluded that the international knowledge base provides valuable input for the development of national guidelines. However, the successful implementation of such guidelines can take place only if they are legitimated and accepted by local key actors and operational target groups. Their involvement during the development process is vital.