A fundamental extension of the classical reliability concept is described. This extension or generalization is necessary to allow the consideration of subjective as well as objective factors in engineering design. Objective uncertainties are treated in explicit probability terms, whereas subjective uncertainties are handled through a “judgment factor” that may be evaluated on the basis of subjective probabilities. The risk of failure then becomes the product of two probabilities. Designs obtained on the basis of this extended reliability concept are not overly sensitive to the required distribution functions; thus, approximate statistical information in terms of means and variances should suffice for practical purposes.