Gerontology is the interdisciplinary study of the biological, social, and psychological aspects of aging, encompassing scholarship from a variety of fields. Although initially focused on the prevention of the physical and cognitive deterioration associated with age, modern gerontology has shifted away from pathologizing aging toward a lifespan perspective that recognizes aging as a part of the normal lifelong developmental trajectory. This entry gives a brief history of gerontology and summarizes the significant biological, social, and psychological theories of gerontology.