This systematic review examines the efficacy of mental health apps for mobile devices (such as smartphones and tablets) in treating various mental health conditions across all ages. The review includes trials that used pre- to posttest designs or compared with control groups, focusing on apps targeting depression, anxiety, substance use, sleep disturbances, suicidal behavior, self-harm, psychotic disorders, eating disorders, stress, and gambling. A comprehensive literature search was conducted in multiple databases from 2008 to 2013. Eight papers describing five apps were included, four of which provided support from mental health professionals. The results showed significant reductions in depression, stress, and substance use, with effect sizes ranging from 0.29 to 2.28 within groups and 0.01 to 0.48 between groups. However, the majority of available apps lack scientific evidence of their efficacy, and further rigorous research is needed to develop and test evidence-based programs. The review highlights the potential of mental health apps to improve treatment accessibility but also underscores the need for public education and industry regulation to ensure the quality and safety of these technologies.This systematic review examines the efficacy of mental health apps for mobile devices (such as smartphones and tablets) in treating various mental health conditions across all ages. The review includes trials that used pre- to posttest designs or compared with control groups, focusing on apps targeting depression, anxiety, substance use, sleep disturbances, suicidal behavior, self-harm, psychotic disorders, eating disorders, stress, and gambling. A comprehensive literature search was conducted in multiple databases from 2008 to 2013. Eight papers describing five apps were included, four of which provided support from mental health professionals. The results showed significant reductions in depression, stress, and substance use, with effect sizes ranging from 0.29 to 2.28 within groups and 0.01 to 0.48 between groups. However, the majority of available apps lack scientific evidence of their efficacy, and further rigorous research is needed to develop and test evidence-based programs. The review highlights the potential of mental health apps to improve treatment accessibility but also underscores the need for public education and industry regulation to ensure the quality and safety of these technologies.