Assessment and treatment of acute responses to traumatic stress has received much attention since September 11, 2001. This article elucidates principles of early intervention with adults in the immediate (within 48 hours) and early recovery phase (within the first week). The principles have been drawn from research on risk and recover factors, stress and traumatic stress theory, and expert consensus recommendations. The debriefing model is discussed, and principle interventions of psychological first aid, pharmacology, and mass trauma systems are described. This article concludes with brief guidelines for longer-term interventions and recommendations for future research.