Public health law is an emerging field in U.S. public health practice. The 20th century proved the indispensability of law to public health, as demonstrated by the contribution of law to each of the century's 10 great public health achievements. Former CDC Director Dr. William Foege has suggested that law, along with epidemiology, is an essential tool in public health practice. Public health laws are any laws that have important consequences for the health of defined populations. They derive from federal and state constitutions; statutes, and other legislative enactments; agency rules and regulations; judicial rulings and case law; and policies of public bodies. Government agencies that apply public health laws include agencies officially designated as "public health agencies," as well as health-care, environmental protection, education, and law enforcement agencies, among others.