Background: While Internet- and mobile-based interventions (IMIs) are potential options to increase the access to evidence-based therapies for post-traumatic stress disorder (PTSD), comprehensive knowledge on their working mechanisms is still scarce. Objective: We aimed to evaluate studies investigating the efficacy and mechanisms of change in IMIs for adults with PTSD. Method: In this systematic review and meta-analysis (PROSPERO CRD42019130314), five databases were consulted to identify relevant studies, complemented by forward (i.e. citation search) and backward...