The aim of this study is to establish and perfect the China Cognition and Aging Study (China COAST) cohort, to clarify the epidemiology, influencing factors, genetic characteristics, pathogenesis, disease characteristics and diagnosis and treatment status of dementia and its subtypes in China. It is of great significance to establish a relatively comprehensive national database of cognitive disorders, improve the clinical diagnosis and treatment level of cognitive disorders, and formulate prevention and treatment strategies for dementia. The primary aims of China COAST are as follows: To use the prospective cohort to establish a large database research platform, so as to provide comprehensive epidemiological data, clinical and neuropsychological evaluation data, biological samples, and laboratory tests and imaging data. To update the prevalence and incidence rate of dementia and its subtypes every 2-3 years, and clarify the conversion pattern from normal elderly to MCI and from MCI to dementia. To explore the known or unknown protective and risk factors of dementia and its major subtypes (AD, VaD, other dementia). To discover new pathogenic genes and susceptible genes of dementia and its major subtypes (AD and VaD), as well as new mutation sites of known pathogenic genes. To study the genetic variation, mutation and polymorphism of PSEN1, PSEN2, APP and APOE genes in dementia patients, and to understand their distribution and roles in the pathogenesis. To study the biomarkers (body fluid, genetics, imaging) with diagnostic value of MCI, AD (sporadic and familial) and VaD, to define their cut-off values, and to establish prediction models. To study the diagnostic criteria of cognitive normal, MCI, dementia and their subtypes (clinical and molecular subtypes) in the cohort, and to make psychological assessment scales with high sensitivity and specificity, and in line with the characteristics of Chinese people. To find potentially modifiable risk factors for dementia and to study the prevention and intervention effect of non-pharmacological treatment on APOE ε4 carriers, MCI and AD or other dementia patients，which included improvements in education, nutrition, health care, and lifestyle changes. This needs a long time follow-up. To explore the relationship between dementia as well as its major subtype AD and cerebral and systemetic circulatory disorders (for example, mixed dmentia), as well as potential therapeutic strategies. To carry out investigation and researches about dementia related education, improve the awareness of dementia, and strengthen the management of dementia. To investigate the level of stigma and discrimination and its influencing factors in patients with Alzheimer's disease and their caregivers.