This article addresses different aspects of the predementia stage of cognitive disorders of mainly neurodegenerative genesis. Current views of the pathophysiology of the initial stages of cognitive disorders are considered, along with the potential use of in vivo markers for pathological amyloidosis and neurodegeneration. Use of the concept “initial signs of cognitive disorder” is proposed. An algorithm for the complex early diagnosis of cognitive disorders is suggested, and the possibilities and perspectives for clinical-neuropsychological, laboratory, and neuroimaging investigation methods are discussed. Data on the main diseases linked with impairment to cognitive functions are presented. The perspectives for using new highly informative methods for the early differential diagnosis of Alzheimer’s disease and vascular cognitive dementias are evaluated.