After being convicted under a municipal ordinance, Olivier brought a Section 1983 action seeking prospective relief against future enforcement of the law. The lower courts held that Heck v. Humphrey barred the suit because success would imply the invalidity of the earlier conviction. The Supreme Court reversed. Heck limits civil claims whose success would necessarily undermine an outstanding criminal judgment, but a request directed solely at preventing future enforcement need not invalidate the past conviction. Because Olivier’s forward-looking constitutional challenge could be adjudicated without setting aside his completed prosecution, the action was not categorically barred. The case was remanded.