Until about a decade ago it was not possible to probe into the types of changes that occur in eukaryotic genes, due to their enormous complexity The use of genetic engineering techniques, however, is beginning to unravel the changes that occur in the genes as an organism ages: such as the changing expression of specific genes under normal conditions and under various types of stress, the changes in the regulatory roles of the sequences in the promoter regions of genes, conformational changes that may occur in genes during aging, and the protein factors that are involved in the aging process. The author presents basic information on eukaryotic genes and follows this with details of the changes that occur in their structure and function during aging.