An opportunity theory of criminal victimization is proposed, focusing on the mediating role played by five risk factors: exposure, guardianship, proximity to potential offenders, attractiveness of potential targets, and definitional properties of specific crimes themselves. Propositions are derived pertaining to the bivariate and multivariate-partial (main) effects expected from the theory and tested in analyses based on a representative sample of the U.S. population for the crimes of assault, burglary, and personal larceny. These data indicate that the relationship between the dimensions of social stratification and the offenses studied here is complex, and that, other things being equal, those usually thought to be most vulnerable economically and socially - the poor, the nonwhite, the old - are not the most likely victims of crime. Race has little direct effect on victimization risk, while age is inversely related to each type of crime at both the bivariate and multivariate levels of analyses. The findings are largely consistent with the proposed theory. (Author abstract)