A sunset law is a law that states that a certain government program, benefit, agency, etc., will finish on a certain date, and will go out of effect unless it is put back into place. Sunset laws became common as both the federal and state governments grew steadily after the 1950s.
Often, as time goes on, the need for certain programs or policies sometimes ceases to exist. For example, a government policy that was implemented during the Cold War may have no use today. Due to the changing needs of the federal and state governments, sunset laws help to make sure that money is not being wasted funding outdated programs, or that the government is not behind the times with its rules and regulations. Periodic re-authorization requirements for laws gives the government the opportunity to make sure that certain policies, laws, agencies, etc. still need to be in existence.