Abstract On the great occasion of Professor Ancel Keys' 100 th birthday (26 January, 2004), it is particularly appropriate — and highly relevant for today and tomorrow — to note the highlights of his professional accomplishments and contributions: the Seven Countries Study (SCS) he initiated and led demonstrated unequivocally in its cross-population analyses that dietary saturated fat intake significantly influences serum cholesterol and the risk of coronary heart disease (CHD), and in turn serum cholesterol relates to CHD risk. In SCS analyses on the several thousand individual participants, it further showed that serum cholesterol, blood pressure, and cigarette smoking all have a continuous, graded, strong, independent, predictive relation to long-term CHD. These data have been critically invaluable for the definition of the major coronary risk factors and low risk status. In scores of metabolic ward feeding trials, Keys and colleagues also demonstrated that dietary saturates and cholesterol relate positively to serum cholesterol, polyunsaturates inversely, and they derived the predictive equation bearing Keys' name. They further showed that increased dietary fiber and weight loss by obese people contribute to reduction of serum cholesterol. All these data served importantly for the development of sound public policy for CHD prevention, and Keys — along with many colleagues all over the world whom he trained and inspired — pioneered in the struggle to achieve and apply that policy in modern public health and medical care.