Mild cognitive impairment (MCI) is the intermediate stage between the cognitive changes of normal aging and dementia. MCI is important because it constitutes a high risk group for dementia. Ideally, prevention strategies should target individuals who are not even symptomatic. Indeed, the field is now moving towards identification of asymptomatic individuals who have underlying Alzheimer's disease (AD) pathology that can be detected using biomarkers and neuroimaging technologies. To this effect, the Alzheimer's Association and the National Institute on Aging have developed a new classification scheme that has categorized AD into a preclinical phase (research category), MCI due to AD, and dementia of Alzheimer's type. However, there are also ongoing research studies to understand high-risk groups for non-Alzheimer's dementia.