Dementia is a progressive deterioration of cognitive functions such as memory, thinking, and reasoning caused by underlying brain changes. It was first described in the 1st century AD and termed "dementia" in the 18th century. Alzheimer's disease, the most common type, accounts for 50-75% of cases. Dementia is diagnosed based on cognitive assessments and is staged based on severity of symptoms from normal forgetfulness to severe impairment requiring full time care. Management involves treating underlying causes, minimizing risks, and providing support to patients and their caregivers.