Aging increases the probability of sickness – Alzheimer's, cancer, cardiovascular disease and all the rest. This chapter recognizes how the molecules that are the building blocks of life – proteins and DNA – are vulnerable and not easily replaced. It explores how there are different mechanisms of aging going on at different levels of the body. A similar mechanism of physical aging is glycosylation. Aging may require us to look at epigenetics, that is, the variations in cellular behavior and physiological traits that come about because of environmental forces that switch on the genes in the cells. The organs of the reproductive system after midlife show dramatic signs of aging: prominently menopause and the end of fertility for females. Caloric restriction is the reduction in the amount of daily calorie intake, a process that has evidently slowed the rate of aging in invertebrates, birds and mammals.