Anyone who has ever interpreted a cross-sectional image of the human brain knows that the wrinkles associated with old age run deeper than the skin. Indeed, widening of the grooves (sulci) within the cerebral cortex, along with enlargement of the fluid-containing spaces (ventricles) deep within the brain, are ubiquitous findings of age-related brain volume decline in neuroradiology. Yet, unlike old-age wrinkles, volume decline in the human brain may begin as early as age 5 and progresses steadily across the life-span, with dramatic acceleration in cases of neurodegenerative diseases, such as Alzheimer's. This book is motivated by the questions of how and why brain volume declines. Through descriptions of multiple experiments designed to relate loss of brain volume with normal aging, Alzheimer's disease, and socioeconomic status, a multiple factor framework is developed by which to further study the aging brain.