[20190815]IF11293_追溯立法：国会入门.pdf

https:/crsreports.congress.gov August 15, 2019Retroactive Legislation: A Primer for CongressBlacks Law Dictionary defines a retroactive law as a law “that looks backward or contemplates the past, affecting acts or facts that existed before the act came into effect.” While Congress often considers legislation that would apply retroactively, the Constitution imposes some limited constraints on such laws. This In Focus outlines those legal constraints on Congresss power and key considerations for Congress related to retroactive legislation. (Related Constitutional provisions that apply only to state legislation, such as the Contracts Clause, are not discussed here.) Retroactive Punishment Laws that retroactively impose punishment raise unique questions under the Constitution, particularly with respect to the Ex Post Facto and Bill of Attainder Clauses. Those provisions (and analogous provisions that apply to the states) prohibit enactment of certain laws that are penal in nature, regardless whether they are styled as criminal laws. Ex Post Facto Clause The Ex Post Facto Clause, contained in Article I, Section 9, Clause 3 of the Constitution, provides: “No . . . ex post facto Law shal