The chapter covers the period from the 1940s, when medical and lay awareness of the increasing incidence of CHD began to grow, to 1985, the year the National Cholesterol Education Program (NCEP) began its widespread and concerted effort to sell the anti-fat, anti-cholesterol message to the nation. This campaign marked a victory for advocates of fat reduction over skeptics who, for decades, continued to question the efficacy of low fat diets as a means of preventing disease. To make sense of the scientific knowledge, its policy ramifications, and the controversy as a whole, it is useful to divide the knowledge linking fats, cholesterol and heart disease into three separate but related hypotheses. These are (1) that higher serum cholesterol levels are associated in some way with an increased risk of CHD, (2) that serum cholesterol levels can be reduced by modifying the fat and cholesterol content of the diet, and (3) that a cholesterol-lowering diet will reduce the risk of developing cardiovascular disease. By the mid-1960s, scientists had established the validity of hypotheses 1 and 2. However, hypothesis 3 remained problematic. While scientists struggled to test its validity, public, commercial and political interest in the link between diet and disease intensified, stimulating the creation of policy before the issue was resolved to everyone’s satisfaction. The history of dietary policy in post-war America provides a fascinating insight into the way science, culture, economics and politics intertwine with policy-making in the field of public health.