Although efforts to prevent posttraumatic stress disorder (PTSD) have met with relatively limited success, theoretically driven preventive approaches with promising efficacy are emerging. The current article critically reviews investigations of PTSD prevention programs that target persons at risk for being exposed to a traumatic event or who have been exposed to a traumatic event. This review uniquely extends prior reviews in this area by using theories of PTSD to suggest future directions in the area of PTSD prevention. The authors first discuss the primary mechanisms of action believed to account for the failure for PTSD symptoms to remit among a substantial minority of traumatic event-exposed individuals. Second, empirical progress in PTSD prevention efforts is reviewed. Third, the authors consider how existing prevention programs target these mechanisms of action. Finally, the authors consider directions for future research in the area of targeted PTSD prevention. (Contains 1 figure.)