This volume assesses formal methods for the quantitative estimation and prediction of human cancer risks. Quantitative estimates of cancer risk can be expressed in different ways. In some cases, estimates of risk under conditions prevailing in the original data are of primary interest; in others, predictions of risk under other conditions are required. Estimates of risk may be based on empirical models that provide a reasonable description of the available data, or on models developed on the basis of plausible assumptions about the mechanisms of carcinogenesis. Throughout this volume, established scientific principles of carcinogenesis are used to support methods proposed for the quantitative estimation and prediction of risk.