Most people likely think of the U.S. Congress and their state and local legislative bodies as the source of most law in this nation. However, this is not true. Today, the bulk of law is made by agencies, not legislative bodies. Congress may enact only a couple hundred laws in a year, whereas the total number of rules promulgated by agencies is in the thousands. Several presidents have attempted to reduce the size of the federal administrative state, all without success.

Many of these regulations affect only a small number of people and businesses. Others regulate more broadly. In aggregate, the total regulations of federal, state, and local agencies greatly affect the lives of all people. Accordingly, an understanding of administrative discretion to make rules is an essential aspect of administrative law.