Genetic instability is widely thought to be involved in the process of aging. Evolutionary theory suggests that aging may well result from stochastic damage to DNA. However, studies of the dynamics of accumulation of simple somatic mutations have shown that such a mechanism cannot readily account for experimental observations. A more complex mutational theory of aging is emerging which allows for interaction between mutations, for damage to epigenetic controls on gene expression, and for interaction of (epi)genetic changes with other possible molecular events contributing to aging.