Dementia, or major neurocognitive disorder, is defined as a decline in 1 or more cognitive domains that causes impairment in everyday function. Alzheimer disease is the most common type of dementia in the United States, with an estimated 6.9 million adults who have Alzheimer disease and are 65 years or older. This article discusses the latest findings in preventing cognitive decline. It also discusses dementia screening, diagnosis, treatment, and the quality of life for persons with dementia and their caregivers.