'Straight' probationary sentences (i.e. sentences that require no form of confinement) will be reduced significantly. Probationary sentences will decline dramatically for serious crimes, such as drug offenses and crimes against persons. For crimes like property offenses, the proportion of sentences involving some form of probation will not change appreciably. Average time served for violent offenses will increase substantially, and Federal prison populations will grow markedly by the end of this century, but not directly as a result of the guidelines. A history of sentencing guidelines and questions answered by the Sentencing Commission Chairman are included. 3 figures.