This article offers an overview of Alzheimer disease (AD) and its differential diagnosis from other dementias. After completing it, readers will: Be familiar with the prevalence of AD and other dementias. Summarize the major causes of dementia. Understand the basic pathology of AD. Recognize the common cognitive and noncognitive symptoms of AD. Identify the risk factors for AD and methods to prevent the disease. Describe the evaluation and diagnosis of AD. Discuss the role of structural and functional imaging in dementia diagnosis. Know how physicians manage AD symptoms. Assimilate this knowledge for use in encounters with patients with Alzheimer disease.