Animals used in aging research are generally of three genetic types- outbred, inbred, and hybrid. These three types have differing uses and characteristics. Outbred animals are heterozygous at many genetic loci and all individuals are genetically unique. Inbred animals are homozygous at all loci and genetically identical to one another. F1 hybrids are heterozygous at many loci, but genetically identical. Both theoretical and empirical findings suggest that each of these models behaves somewhat differently with respect to aging. This presentation will detail these theoretical and empirical findings, and suggest what uses each genetic type might best be put to with respect to aging research.