Dental twinning results from abnormal events in the embryologic development of teeth. This paper describes the impossibility of assigning precise diagnostic terms. such as gemination, fusion, macrodontia, and concrescence, to dental twinning anomalies because the entire course of odontogenesis cannot he witnessed. Traditional nomenclature is reviewed and seven cases that exemplify the principle are presented. Modification of nomenclature to describe dental twinning defects is suggested.