A clause in a statute, regulation or similar piece of legislation that provides for an automatic repeal of the entire or sections of a law once a specific date is reached. once the sunset provision date is reached, the pieces of legislation mentioned in the clause are rendered void. If the government wishes to extend the length of time for which the law in question will be in effect, it can push back the sunset provision date any time before it is reached.

The purpose of a sunset provision is generally to allow lawmakers to institute a law when change or government action is required reasonably quickly, when the long-term ramifications of the law in question are difficult or impossible to foresee, or when circumstances warrant such a legal structure.

A good example of legislation warranting a sunset provision is the U.S.A. Patriot Act. Intended to address relatively short-term security concerns following the events of September 11, 2001, the act, when it was initially drafted, included a sunset provision for December 31, 2005.