The primary task set for the U.S. Sentencing Commission by the Sentencing Reform Act of 1984 was to promulgate mandatory sentencing guidelines that structure the discretion of Federal judges. This structuring of judicial discretion is designed to reduce sentencing disparity that undermines "equal justice under law." The introduction to this article defines judicial discretion and underscores the terms of recent calls for reform in this area. The author then discusses the historical shifts in sentencing goals in various major cultures of world history, followed by a historical summary of sentencing goals from colonial America to the present. The author then turns to an overview of the Sentencing Reform Act of 1984, the enabling legislation for the creation and work of the U.S. Sentencing Commission. Key specific directives given to the commission by the act are outlined. Following the implementation of the sentencing guidelines formulated by the commission in 1987, the first challenge to their constitutionality came in Mistretta v. United States (1989) before the U.S. Supreme Court. The rationales for challenges to the guidelines and the Court's upholding of their constitutionality are explained. Following an elaboration of the bases for the major decisions reflected in the first promulgation of the guidelines, the article concludes with an explanation of the U.S. Sentencing Commission's commitment to future monitoring, evaluation, and revision of the guidelines. 306 footnotes