Studies of diseases associated with cognitive impairment have been undertaken since ancient times, at the dawn of medical science. Initially, the main focus was on the connection between higher cortical function disorders and age-related changes. This approach has been used for many centuries. In the 19^th century, as neurology, anatomy, morphology, and other disciplines developed, it became clear that dementia is associated with specific changes in brain structure. At the beginning of the 20^th century, Alzheimer’s disease was recognized as a distinct nosological entity, with descriptions of its classical clinical manifestations, extracellular amyloid inclusions, and intracellular neurofibrillary tangles. Such a clinical and morphological approach prevailed over the next few decades. However, it was not until the 1980^s that sufficiently clear criteria for the disease were established. The main priority was dementia in Alzheimer’s disease. In addition, the definitive diagnosis was possible only on the basis of pathomorphological examination of brain tissue samples. Clearly, this situation cannot meet the current needs of both clinicians and the scientific community, especially given the diagnostic trend toward early verification of the pathological process. Therefore, research in this direction continued, and at the beginning of the 21^st century, several diagnostic criteria were proposed based on methods for detecting Alzheimer’s disease at predementia stages. There is a gradual shift in priority from clinical evaluation to laboratory and neuroimaging biomarkers. It allows us to consider Alzheimer’s disease a biological process characterized by specific biochemical changes in the brain manifested long before the onset of distinct symptoms.