This book describes some of the theories of biological aging and the evidence for those theories. The topics included are those on defining aging, model systems for studying aging, the effect of environmental temperature, the genetic basis of aging, protective enzymes, free radicals, lipid peroxidation, antioxidants, singlet oxygen, iron, cadmium, chelators, copper, aluminum, Alzheimer's disease, chromium, lead, boron, neutrons, light, exercise, anti-inflammatory agents, vitamin A, and mercury. The books ends with speculations on how all these factors might affect the human aging process.