This chapter deals with the occurrence, determinants and primary prevention of dementia. Dementia is one of the major causes of functional dependence, poor quality of life, institutionalisation and mortality among elderly people. The risk of dementia increases almost exponentially with advancing age. As the population ages, dementia poses a serious threat to public health and social welfare system of our society. Accumulating evidence suggests that cardiovascular risk factors significantly contribute to the development and expression of dementia. Thus, adequate management of vascular risk factors and related disorders can be one of the preventative strategies against cognitive ageing and dementia. In addition, psychosocial factors such as educational achievement, socially-integrated and mentally-stimulating lifestyles are critical for delaying the onset of dementia by increasing cognitive reserve. Taken together, maintaining vascular health and adopting a healthy cognitive lifestyle from a life-course perspective may be the most promising strategy to achieve late-life cognitive health.