Digital technology has a significant and still growing impact on societies, including well-being of individuals. Various applications of mental health technologies have been developed to address different dimensions of the global mental health challenges. In this chapter we describe the current knowledge of mental health applications, including websites, social media, apps, chatbots, videoconferencing, wearable sensors, and virtual reality. Based on the literature, e-mental health applications have been widely used for various purposes, target groups, settings, and environments. Overall purposes of these applications are to support health and mental well-being by assessing, monitoring, supporting, offering treatment, and evaluating treatment outcomes. Studies have reported promising findings, but further research is still needed to ensure effective, ethical, and safe use of e-mental technology.