Sentencing disparity occurs when similar cases are not disposed similarly or when dissimilar cases are not disposed differently. Disparity implies that many offenders are not being sentenced in accordance with legally relevant factors. Disparity cannot be identified nor analyzed, however, except within a coherent sentencing system that has clear definitions of the aims and criteria for sentencing. Disparity cannot be measured across sentencing systems, since the criteria for normative sentencing will vary according to whether the aims of sentencing are to provide just deserts, rehabilitation, incapacitation, or deterrence. Sentencing disparity only exists when there are variations in sentencing that cannot be explained by factors related to the aims of sentencing. For many, the solution to the disparity problem lies in promoting foreseeability in sentencing by making the reasoning of the sentencing process more uniform. Foreseeability, however, should not be an end in itself, since it may involve a uniform departure from coherent sentencing aims. Disparity must be reduced by providing sentencers with the knowledge required to render sentences in accordance with the factors relevant to the particular sentencing system.