Classification of dementia involves the recognition of its presence, followed by the differential diagnosis of its cause. Informant‐based methods for dementia detection can be highly sensitive, even when cognitive impairment is mild. Alzheimer's disease (AD) is by far the leading cause of dementia; standardized clinical criteria result in high diagnostic accuracy rates. Classification of other dementing disorders is less satisfactory, particularly because there is frequent clinical and pathological overlap with AD. After AD, the most common causes of dementia are vascular dementia and dementia in persons with Parkinson's disease. Less common dementias include progressive supranuclear palsy, Huntington's disease, Pick's disease, Creutzfeldt‐Jakob disease, and inherited metabolic disorders, most of which are extremely rare. Identifying the cause of dementia is important because some forms can be treated with currently available therapies. In instances involving genetically transmitted disease, genetic testing and counseling of family members may be advisa