Neuropsychologists play a leading role in the evaluation of the memory complaints and changes in cognitive functioning that frequently occur in the later decades of life. Although some healthy aging persons maintain very high cognitive performance levels throughout life, most older people will experience a decline in certain cognitive abilities. This decline is usually not pathological, but rather parallels a number of common decreases in physiological function that occur in conjunction with normal developmental processes. For some older persons, however, declines go beyond what may be considered normal and are relentlessly progressive, robbing them of their memories, intellect, and eventually their abilities to recognize spouses or children, maintain basic personal hygiene, or even utter comprehensible speech. These more malignant forms of cognitive deterioration are caused by a variety of neuropathological conditions and dementing diseases.