A historical overview of the landmark Sentencing Reform Act of 1984 and of the Commission's development process provide background for the initial guidelines and policy statement issued in April and May 1987. The report presents additional explanatory information on certain aspects of the guidelines to assist in better understanding their rationale and application. Areas addressed include the approach used to select and determine the offense levels and adjustments, how data on current sentencing practices were analyzed, reasons underlying the criminal history component, and sentencing procedures and plea agreements. Projections in the prison impact report indicate that imposition of the guidelines will significantly reduce the incidence of straight probationary sentences, substantially increase average time served for violent offenses, and have little effect on average time served for most property crimes. Federal prison populations are likely to grow dramatically by the end of the century, but the guidelines will contribute only marginally to such growth. Appendixes contain a list of witnesses at Commission hearings, a comparison of sentencing guideline offense levels with U.S. Parole Commission offense levels, and a table projecting sentence length and time served for defendants.