The significance of human individuality is such that each human functions as a unique "molecular" unit of the mass of humanity. Understanding the natural basis for the uniqueness of the individual has long been an objective. The possibilities have been analyzed by Julian Huxley, by A. E. Needham, by Roger Williams, and by others. With his books Biochemical Individuality and Free and Unequal, Roger Williams has done as much as anyone to focus atten­ tion on this complex of questions. Although scheduled to partici­ pate in this program, Roger Williams* was unable to attend due to illness. He asked, however, that a quotation be included in the proceedings. This quotation from Chraka is presented early in this book. While metabolic bases for individuality have received a con­ siderable investigation and discussion by Williams and others, the case for underlying determinants and derivative consequences have not been examined as fully. The specificities that abound in our living world can be traced to the manner in which molecules fit with each other. While numerous studies having other objectives can be cited in support of molecularly based specificities, a few of the leaders in the development of the understanding of physical aspects of biological information present here some of their latest inferences. Several of the participants discuss some of the conse­ quences at higher levels. Examination of the fascinating cases of reunited identical twins are seen as providing a capstone to the hierarchical treatment.