The measure focuses on the prior record of the offender and includes only variables typically found in a criminal history. Thus, the current offense, the type of defense, the offender's background, and other variables have been excluded from consideration. The result is a provisional composite index of criminality that can be applied to any criminal history so that its relative seriousness can be measured. The paper discusses the four main viewpoints held concerning the use of criminal histories in criminal justice decisionmaking processes and describes the study design in detail. Three models were used to test the index. As currently constructed, the index cannot deal with more than one conviction for the same crime. Tables and footnotes are supplied. (Author abstract modified)