ABSTRACT: INTRODUCTION: Sustained cooperative action is required to improve the mental health of populations, particularly in low and middle-income countries where meagre mental health investment and insufficient human and other resources result in poorly performing mental health systems. THE OBSERVATORY: The International Observatory on Mental Health Systems is a mental health systems research, education and development network that will contribute to the development of high quality mental health systems in low and middle-income countries. The work of the Observatory will be done by mental health systems research, education and development groups that are located in and managed by collaborating organisations. These groups will be supported by the IOMHS Secretariat, the International IOMHS Steering Group and a Technical Reference Group. SUMMARY: The International Observatory on Mental Health Systems is: 1) the mental health systems research, education and development groups; 2) the IOMHS Steering Group; 3) the IOMHS Technical Reference Group; and 4) the IOMHS Secretariat. The work of the Observatory will depend on free and open collaboration, sharing of knowledge and skills, and governance arrangements that are inclusive and that put the needs and interests of people with mental illness and their families at the centre of decision-making. We welcome contact from individuals and institutions that wish to contribute to achieving the goals of the Observatory.Now is the time to make it happen where it matters, by turning scientific knowledge into effective action for people's health. (J.W. Lee, in his acceptance speech on his appointment as the Director-General of the World Health Organization) 1.