Various aspects of the critical examination of dating materials of terrrestrial origin are discussed. The problem of determining the original 14C content of the materials is examined; contamination from the burial site must be taken into account in the calculations. Three situations in which dating anomalies arise have occurred: when prehistoric man has used old carbon, when there have been perturbations of the site contemporaneous with deposition of the sample, and when there have been perturbations of anthropogenic origin.