Project Summary Rising life expectancy is contributing to rapid increases in the size of the older population and is expected to lead to a sharp rise in Alzheimer’s disease and Alzheimer’s disease related dementias from about 47 million people worldwide today, to potentially more than 140 million in 2050. However, recent population studies have found that the incidence of Alzheimer’s disease and Alzheimer’s disease related dementias is lower than that indicated by previous projections in some countries, but greater in others. Lifestyle factors as well as environmental factors might reduce or increase an individual’s risk of developing dementia. We propose to advance our understanding of protective and risk factors for late-life cognitive decline and Alzheimer’s disease and Alzheimer’s disease-related dementias (hereafter referred to as dementia) in China. We propose a novel life-course model of risk factors, building on the recently proposed model by the Lancet commission, which links dementia risk to early and mid-life factors, within the context of historical, institutional, and physical environments, including obesity, diabetes hearing loss, visual impairment, smoking, drinking, depression, physical inactivity, social isolation, and socioeconomic status. Specifically, this project aims to further study early and mid-life personal, family, community, and external factors that may contribute to late-life cognition and dementia risk using new, retrospective life-history interview data in China.