The term: ‘behavioural and psychological symptoms of dementia’ (BPSD) refers to a mixed group of phenomena. BPSD are the non-cognitive features of dementia and include depression, anxiety, psychotic symptoms, apathy, irritability, aggression, and sleep and eating problems. They occur in around 80% of people with dementia at some stage, several of them becoming more frequent as dementia progresses. Some BPSD, notably apathy, are very persistent. BPSD often limit the person’s quality of life and can be stressful for carers. Causes of BPSD include biological, psychological, social, and environmental factors. This chapter explores how they are assessed and measured, and how they may usefully grouped together in symptom clusters. Usually four symptom groups are found: affective symptoms, psychosis, hyperactivity, and euphoria. However, these are not always consistent and in particular apathy does not consistently belong in one group. Approaches to management of BPSD are outlined.