This article charts the historical development of the discipline of global mental health, whose goal is to improve access to mental health care and reduce inequalities in mental health outcomes between and within nations. The article begins with an overview of the contribution of four scientific foundations toward the discipline's core agenda: to scale up services for people with mental disorders and to promote their human rights. Next, the article highlights four recent, key events that are indicative of the actions shaping the discipline: the Mental Health Gap Action Programme to synthesize evidence on what treatments are effective for a range of mental disorders; the evidence on task shifting to nonspecialist health workers to deliver these treatments; the Movement for Global Mental Health's efforts to build a common platform for professionals and civil society to advocate for their shared goal; and the Grand Challenges in Global Mental Health, which has identified the research priorities that, within the next decade, can lead to substantial improvements in the lives of people living with mental disorders. The article ends by examining the major challenges for the field, and the opportunities for addressing them in the future.