By longitudinally following separate cohorts of normal controls without a family history of AD, normal controls with a family history of AD, subjects with mild cognitive impairments and diagnosed dementia subjects, we hope to track the spectrum of AD from its clinical and biologic origins. As a result, this study is both a diagnostic screening protocol and a natural history protocol. It will address a series of important clinical and biological questions among a wide range of normal and diseased individuals and should serve as a basis for the development of biologic markers in AD that could be used for diagnostic and therapeutic purposes in the future. A long-term goal of this protocol to identify markers and eventually individual people who are at increased risk of developing AD before the typical cognitive changes of AD become manifest. In pursuit of that goal, we will also carefully monitor and evaluate the clinical medications taken by our subjects to see if they influence the course of AD.