Police power is the right to protect the country and its population from threats to the public health and safety. The term “police power” predates the development of organized police forces, which did not develop until the postcolonial period. In the colonial period, police power was used to control nuisances, such as tanneries that fouled the air and water in towns, to prevent the sale of bad food, and to quarantine persons who were infected with communicable diseases. Many of the colonies had active boards of health to administer the police power. This was one of the main governmental functions in the colonial period.

Under the Constitution, the states retained much of their police power but share the right to regulate health and safety issues with the federal government. Examples of the federal use of the police power are food and drug regulations, environmental preservation laws, and workplace safety laws. The states have companion laws in most of these areas, plus local public health enforcement such as restaurant inspections, communicable disease control, and drinking water sanitation. In most cases, the states share jurisdiction with the federal government and the courts will enforce whichever is the more strict law. State and local public health laws are exercises of the police power.