With international contributions from Denmark, Peru, Italy, Turkey, Estonia, Russia, Canada, the USA, Australia and the UK, this special issue offers insights and evidence about the technology's ability to act as a force of good and a source of harm for young people's mental health. As we better understand the complex and bidirectional relationship between technology and mental health, we need to move beyond dichotomous narratives about it being good or bad; it is both, depending on how it is used. Collective responsibility across technology companies, researchers, public services and community organisations, parents and the young people themselves can make a difference in the way technology is used to protect and improve mental health.