The chapter discusses the epidemiology of Alzheimer's disease (AD), focusing on its occurrence, determinants, and strategies for intervention. AD is the most common cause of dementia, affecting over 25 million people worldwide, with a prevalence of 6.4% in those aged 65+ years and 4.4% in those with dementia. The incidence rate is 19.4 per 1000 person-years in Europe and 15.0 per 1000 person-years in the US. The disease is strongly associated with aging, and the risk increases with age. Key risk factors include vascular risk factors (e.g., smoking, high blood pressure, obesity) and psychosocial factors (e.g., education, social engagement, physical exercise). Protective factors include high education, active social engagement, and mentally stimulating activities. The chapter also highlights the economic burden of AD, which is estimated to be over $315 billion globally in 2005. Interventions for primary prevention focus on managing vascular risk factors and maintaining socially integrated lifestyles, while secondary prevention aims to detect and manage the disease early. Multidomain interventions, including nutritional guidance, physical activity, cognitive training, and metabolic and vascular risk factor management, are being explored to delay the onset of cognitive impairment and dementia.The chapter discusses the epidemiology of Alzheimer's disease (AD), focusing on its occurrence, determinants, and strategies for intervention. AD is the most common cause of dementia, affecting over 25 million people worldwide, with a prevalence of 6.4% in those aged 65+ years and 4.4% in those with dementia. The incidence rate is 19.4 per 1000 person-years in Europe and 15.0 per 1000 person-years in the US. The disease is strongly associated with aging, and the risk increases with age. Key risk factors include vascular risk factors (e.g., smoking, high blood pressure, obesity) and psychosocial factors (e.g., education, social engagement, physical exercise). Protective factors include high education, active social engagement, and mentally stimulating activities. The chapter also highlights the economic burden of AD, which is estimated to be over $315 billion globally in 2005. Interventions for primary prevention focus on managing vascular risk factors and maintaining socially integrated lifestyles, while secondary prevention aims to detect and manage the disease early. Multidomain interventions, including nutritional guidance, physical activity, cognitive training, and metabolic and vascular risk factor management, are being explored to delay the onset of cognitive impairment and dementia.