All of these are major public health concerns. In the United States system of government, only the states have the right to legislate based on their police power. Police power is used to enact a variety of substantive laws in different areas such as zoning, land use, fire and building codes, gambling, discrimination, parking, crime , professional licenses, alcohol, motor vehicles, bicycles, nuisances, school and health. For example, it is up to the police of a state to enact a law on compulsory vaccination and the legislature can first determine whether the best way to protect and prevent the population against smallpox is vaccination or