Several psychological approaches have been evaluated in the immediate aftermath of trauma to prevent the onset of mental health problems, such as posttraumatic stress disorder (PTSD) and depression. Secondary prevention strategies include interventions offered to all individuals exposed to a traumatic event unselected for their levels of distress or for presence of a clinical diagnosis. For adults, psychological debriefing -or similar brief counseling interventions – were not effective in reducing the development of PTSD, depression or anxiety. Psychological First Aid (PFA) is a modular approach aimed at reducing initial distress and fostering short and long-term adaptive functioning. Although implemented worldwide, there have been no effectiveness studies thus far. Abbreviated versions of evidence-based treatments such as trauma-focused CBT or exposure therapy have been shown effective in reducing the onset or course of PTSD in people identified with acute stress disorder (ASD) or early symptoms of PTSD. Finally, collaborative care interventions, multidisciplinary interventions consisting of case management, and clinician involvement if needed, showed modest effects on PTSD symptoms and alcohol use in injured trauma surgery patients. In conclusion, there are still many important gaps in our knowledge about effectiveness of psychological approaches to prevent mental health problems following trauma. These gaps include a lack of studies on interventions for mental health outcomes other than PTSD (such as daily functioning, and social and community functioning), studies in children, and studies evaluating the cost-effectiveness of early interventions.