Alzheimer's disease (AD) is the most common form of dementia in aging adults. The diagnosis is still primarily made on the basis of history and physical and neurologic examinations. The incidence increases rapidly with age, so the number of affected individuals with AD is ballooning rapidly. Cholinesterase inhibitors are mildly effective in treating cognitive and global functioning, as well as behavior abnormalities in patients with mild-, moderate-, or severe-stage disease. The N-methyl-D-aspartate (NMDA) antagonist memantine is similarly mildly effective alone or in combination with cholinesterase inhibitors in moderate to severe stages of the disease. No therapy is proven to delay disease progression, but recent insights into the pathophysiology of AD have led to promising investigational therapies, including the development of both γ- and β-secretase inhibitors as well as active and passive immunization against the amyloid β-protein. Continuum Lifelong Learning Neurol 2007;13(2):39-68.