The world is facing an unprecedented range of emergencies. In reaction to these complex adversities, many people experience considerable distress and impairment, and a minority may even go on to develop mental health conditions. Meanwhile, those with pre-existing mental health conditions may experience a worsening of their condition and are at risk of neglect, abandonment, abuse and lack of access to support. Unfortunately, evidence-based mental health care is often extremely limited in humanitarian settings. In response, the World Health Organization (WHO) and the United Nations High Commissioner for Refugees (UNHCR) published the Mental Health Gap Action Programme (mhGAP) Humanitarian Intervention Guide (mhGAP-HIG) in 2015. This practical tool supports health-care providers in assessing and offering first-line management of mental, neurological and substance use (MNS) conditions in humanitarian emergency settings. 2 December 2021. The current report, Stories of change from four countries: Building capacity for integrating mental health care within health services across humanitarian settings, describes efforts in four countries to build evidence-based mental health systems in humanitarian emergency settings using the mhGAP-HIG. This report includes three sections, the first describing the importance of scaling up mental health care in emergency contexts, the second outlining case studies (“stories of change”) to scale up the Mental Health Gap Action Programme (mhGAP) programme in four settings and the third describing lessons learned by stakeholders.