Patients with delirium, dementia, and those with both delirium and dementia can be the most challenging patients in the emergency department (ED). Integration of psychiatric emergency services into the ED can help with cognitive assessment and management. Patients can also have delirium superimposed on dementia, making diagnosis and management more challenging. Although delirium can occur in patients across the lifespan, most studies have focused on older adults, as does this chapter. The most popular instruments for efficient screening of patients have been the Mini-Mental State Examination (MMSE), Confusion Assessment Method (CAM), CAM-ICU, Six-Item Screener (SIS), and the Mini-Cog. Treatment strategies for managing delirium are divided into non-pharmacologic and pharmacologic interventions and can definitely be implemented in the ED. Alzheimer's disease is the most common form of dementia, accounting for 50-80% of cases. The neuropsychiatric sequelae of dementia can make the diagnosis of a presenting patient more challenging.