Criteria for the diagnosis of Alzheimer’s disease were established in 1984 by the National Institute of Neurological and Communicative Disorders and Stroke (NINCDS) and the Alzheimer’s Disease and Related Disorders Association (ADRDA). Commonly used since their implementation, these criteria are becoming obsolete for everyday practice, and a review is being claimed. Three groups of experts consisting of renowned experts from the National Institute on Aging (NIA) and the Alzheimer’s Association proposed a set of recommendations to modify the criteria in this field of research. Two notable differences from the initial criteria were included: the incorporation of biomarkers and the formalization of different disease stages in the diagnostic criteria. From now on, mild cognitive impairment is incorporated in the diagnosis as another stage of dementia. However, the new criteria are still under revision and are currently of use for research purposes with the aim to get the definitive modification for the clinical criteria. This chapter presents the main developments in research concerning Alzheimer’s disease and mild cognitive impairment to define these new research criteria.