The WHO MONICA Project is a multicentre international collaborative project coordinated by the World Health Organization. Its objective is to measure trends in cardiovascular mortality and morbidity and to assess the extent to which these trends are related to changes in risk factor levels and/or medical care, measured at the same time in defined communities in different countries. Thirty-nine collaborating centres from 26 countries of Europe, North America, and the Western Pacific collaborate in this project, using a standardized protocol and covering a population of approximately 10 million men and women aged 35-64. The WHO MONICA Project is directed by the Council of Principal Investigators and a Steering Committee, and it is managed by a Management Centre, Data Centre, Quality Control Centres (for event registration, ECG coding and lipid determinations) and Reference Centres (for optional studies). The MONICA methodology is increasingly used as a measurement tool for cardiovascular and non-communicable diseases prevention and control programmes by centres within and outside the project.