Prevention is better than cure.

—Desiderius Erasmus

Preventing disease involves a wide range of interrelated programs, actions, and activities. Some prevention measures are sweeping global policy initiatives, such as national and state government actions to reduce health risks by limiting air pollution and other toxic exposures or standards to assure the safety of food and water supplies. Others are focused efforts of public health professionals and agencies, such as the National Institutes of Health (NIH) Office of Disease Prevention, Centers for Disease Control and Prevention (CDC), and the American Cancer Society, to reduce the incidence (occurrence of new cases) of specific diseases such as heart disease, diabetes, and lung cancer.

The effectiveness of global and local disease prevention programs largely depends on the extent to which individuals take personal responsibility for their own health by avoiding health risks such as tobacco use, substance abuse (misuse of alcohol and drugs), and unsafe sex. People who eat healthy diets; get adequate exercise and rest; wear seatbelts in automobiles and helmets on bikes, motorcycles, scooters, and the like; successfully manage stress; and maintain positive outlooks on life are on the front lines of disease prevention. Similarly, individuals who effectively use health care resources by obtaining recommended immunizations, physical examinations, and health screenings are actively working to prevent disease and disability.

Prevention involves governments, professional organizations, public health professionals, health care practitioners (physicians, nurses, and allied health professionals), and individuals working at three levels to maintain and improve the health of communities. One level, known as primary prevention, is inhibiting the development of disease before it occurs. Secondary prevention, also called "screening," refers to measures that detect disease before it is symptomatic. Tertiary prevention efforts focus on people already affected by disease and attempt to reduce resultant disability and restore functionality.