The United States has 50 state legal systems and one federal legal system, and each system has three major subdivisions. Individual public health practitioners have to be aware of the laws of the state they practice in and the federal laws applicable to their practice. National programs must deal with federal rules and the laws of every state they does business in. What is most surprising to a layperson is that these state laws can be dramatically different, with some states criminalizing what other states encourage.