Rule of Law (foaled 6 March 2001), is a retired World Champion Thoroughbred racehorse and active sire who was bred in the United States but trained in Britain. In a career which lasted from June 2003 until September 2004, he ran nine times and won four races. He recorded his most important victory when winning the Classic St. Leger Stakes on his final racecourse appearance. He had previously finished second in the 2004 Epsom Derby.