Dr Mark van Ommeren is head of the mental health unit within the WHO Department of Mental Health and Substance Use. Much of Mark’s work has been inter-agency and focused on: initiating and developing humanitarian policy (ie Sphere standards, IASC guidelines), humanitarian tools (eg assessment tools, psychological first aid (PFA) guide, mhGAP Humanitarian Intervention Guide); evidence-based WHO guidelines (eg on depression and PTSD) ; scalable psychological interventions (eg Problem Management Plus); WHO model Essential Medicines List update, and supporting countries to build back better mental health systems after emergencies. To improve intersectoral collaboration he introduced the now popular term “mental health and psychosocial support (MHPSS)” into inter-agency (IASC) humanitarian policy.