After World War II coronary heart disease (CHD) assumed epidemic proportions in western countries. In many countries the peak of the epidemic occurred in 1968. In 1978 the National Heart, Lung and Blood Institute of the NIH organized the Bethesda conference on the decline in CHD mortality. The aim of the conference was to find out whether measures of prevention or improvements in acute coronary care were responsible for the decline in age-specific CHD mortality rates. Because of lack of appropriate data in 1978 these questions remained unanswered. To answer these questions the WHO MONICA (Monitoring trends and determinants in cardiovascular disease) project was organized as a monitoring system to assess trends and determinants of cardiovascular mortality, incidence and case fatality from the mid 1980 s to the mid 1990 s in 38 populations in 21 countries worldwide. Altogether some 13 million people were monitored over a 10 year period. 166,000 myocardial infarction patients were registered and more than 300,000 men and women were sampled and examined for their cardiovascular risk factors and many other health data. In Western countries, where the CHD mortality decline was on average 2-3 % annually, two thirds of this decline could be explained by a decline in CHD incidence and one third by a decline in CHD case fatality. When relating risk factor changes to changes in CHD event rates in men over a time period of 10 years in all MONICA populations it turned out that the greatest contribution to the CHD decline came from a decrease in smoking. On a worldwide scale the Seven Countries Study, the Framingham Heart Study and the WHO MONICA Project have contributed most to the development of epidemiology and prevention of cardiovascular diseases.