Abstract: The criminal sentence seeks to reduce the frequency and severity of crimes by employing the following mechanisms: (a) isolating the convicted criminal from the rest of the population, so that he is unable to commit crimes during the period of his enforced isolation; (b) punishing the con victed prisoner, so that he—and others contemplating crime —will be deterred by the prospect of a painful response if convicted; (c) rehabilitating the convicted criminal, so that his desire or need to commit future crimes will be diminished. During different periods of our history, the power to deter mine the duration of a convicted criminal's sentence has been allocated to different agencies: first to the legislature; then to the judiciary; and now—under indeterminate sentencing—to the parole board. The locus of sentencing authority has a con siderable effect on such factors as the length of sentences, the degree of discretion, and the disparity among sentences. The century-long trend in the direction of indeterminancy seems to be ending. It is likely that the coming decades will witness a return to more legislatively-fixed sentences.