Aging is a natural biological and physiological phenomenon resulting in decline in the function of our body’s organ system. Aging might take place due to many reasons such as genetic factors, environmental factor, unhealthy lifestyle, the kind of food we intake, tissue damage, and decline in the cellular function that results in senescence, oxidative damage, and DNA modification. There are many factors that determine the physiological age such as proper diet, good exercise, pleasant sleeping habits, healthy food, mental health, and a well-functioning body. There are four kinds of aging: biological aging, chronological aging, pathological aging, and physiological aging. In this chapter, we will discuss about the physiological aging of organ and tissues of the human body.