Prevention of disease is the only method to substantially reduce morbidity and mortality in a population. The two key determinants of disease are the levels of risk factors/determinants and the adherence to efficacious therapies, and there are two approaches to these: public health and preventive medicine. Clinical trials remain the cornerstone for evaluating new approaches. Effectiveness studies are required to evaluate the best approaches to deliver efficacious therapies; public health and preventive medicine programs must include the entire population, and can be costly. Environmental changes have greater benefits and a greater likelihood of reaching large segments of the population, but the preventive medicine approach is better for high-risk diseases. New risk factors and diseases evolve from the upper to lower social classes, while preventive therapies evolve from the upper. to lower education groups.