The digital revolution is evolving at an unstoppable pace. Alongside the unprecedented explosion of digital technology facilities and systems, mental health care is under greater pressure than ever before. With its emphasis on big data, computing power, mobile technology and network information, digital technology is set to transform healthcare delivery. This article reviews the field of digital health technology assessment and intervention primarily in secondary service mental healthcare, including the barriers and facilitators to adopting and implementing digitally-mediated interventions in service delivery. We consider the impact of digitally-mediated communication on human interaction and its potential impact on various mental states such as those linked to mood, anxiety but also well-being. These developments point to a need for both theory- and data-driven approaches to digital healthcare. We argue that, as developments in digital technology are outpacing the evaluation of rigorous digital health interventions, more advanced methodologies are needed to keep up with the pace of digital technology development. The need for co-production of digital tools with and for people with chronic and mental health difficulties, and implications of digital technology for psychotherapy practice, will be central to this development.