Dementia is characterised by memory loss (initially of recent events), loss of executive function (such as the ability to make decisions or sequence complex tasks), other cognitive deficits, and changes in personality. This decline must be serious enough to affect social or occupational functioning, and reasonable attempts must be made to exclude other common conditions, such as depression and delirium. Alzheimer's disease is a type of dementia characterised by an insidious onset and slow deterioration, and involves impairments in memory, speech, personality, and executive function. It should be diagnosed after other systemic, psychiatric, and neurological causes of dementia have been excluded clinically and by laboratory investigation. more. Vascular dementia is often due to multiple large or small vessel disease. It often presents with a stepwise deterioration in cognitive function with or without language and motor dysfunction. It usually occurs in the presence of vascular risk factors (diabetes, hypertension, arteriosclerosis, and smoking). Characteristically, it has a more sudden onset and stepwise progression than Alzheimer's disease, and often has a patchy picture of cognitive deficits. Lewy body dementia is a type of dementia that involves insidious impairment of cognitive function with parkinsonism, visual hallucinations, and fluctuating cognitive abilities. Night-time disturbance is common and there is an increased risk of falls.[1][2] Careful clinical examination of people with mild to moderate dementia and the use of established diagnostic criteria accurately identifies 70% to 90% of causes confirmed at post mortem.[3][4] In all types of dementia, people will experience problems with cognitive functioning and are likely to experience behavioural and psychological symptoms of dementia. Where possible, we have divided outcomes into cognitive or behavioural/psychological, although there is often considerable crossover between these outcomes, both clinically and in research. This review deals solely with people with Alzheimer's disease, Lewy body dementia, or vascular dementia.