Access to effective interventions aimed at reducing the mental health consequences of exposure to traumatic events is hampered by barriers to treatment. Mobile applications (apps) are one way to overcome these barriers. However, the effectiveness of apps in reducing posttraumatic stress symptoms (PTSS) is limited, which could be explained by low user engagement. A better understanding of the needs and preferences of individuals with PTSS could help in developing apps that are more engaging and possibly more effective. This review aims to synthesize qualitative findings from studies examining the subjective experiences of individuals who use apps for PTSS. A systematic search was conducted in Pubmed and APA PsycInfo. Empirical studies that report qualitative data and focus on one or more apps designed for the self-assessment or the self-management of PTSS were included. Sixteen articles focusing on 14 apps met the inclusion criteria. Participants reported barriers (e.g., lack of perceived benefits), facilitators (e.g., ease of use), benefits (e.g., improved mental health), and adverse effects (e.g., increased symptoms) related to the use of the apps. They also made suggestions aimed at improving user experience, such as increasing customization. In conclusion, developing apps with a user-centered approach, promoting social support through the use of the apps, and including gamification elements might increase user engagement with apps for PTSS. Further research should test if that is the case.