Of the broad spectrum of brain diseases that can produce dementia, Alzheimer's disease (AD) is the most common. AD is a devastating disorder characterized by progressive loss of memory and intellectual abilities, affecting more than 40% of individuals older than 85 years of age. The remarkable increase in disease prevalence that has accompanied the growth of the oldest segment of the population has heightened public awareness and accelerated research efforts to understand the disease. AD has been recognized as a clinical and neuropathological entity for more than 100 years, but specific therapies were unavailable until the development of the first cholinesterase inhibitor, tacrine, about 20 years ago. Since that time, several new cholinesterase inhibitors have been approved for the treatment of AD patients, and novel therapies, such as the N-methyl-d-aspartate (NMDA) receptor antagonist memantine, have shown modest benefit in improving cognitive function in patients with AD. Common clinical practice has also embraced the use of high-dose vitamin E as an antioxidant that may provide some neuroprotective benefit. Research on AD funded by the government, private foundations, and the pharmaceutical industry commits billions of dollars annually for achieving better understanding of the disease and for developing more effective treatments. These efforts will inevitably lead to continued improvement in clinical practice in the coming years.