Emil Kraepelin formulated the initial nosology of Alzheimer’s disease in the first decade of the 20th century. Nowadays, clinical and pathological presentations (including those associated with primary progressive aphasia, posterior cortical atrophy, Lewy body disease, or Down syndrome) continue to evolve. Nevertheless, Kraepelin started the process of defining Alzheimer’s disease as a discrete disease entity and, as such, the disease logically fits within our current notions of nosology in which most, if not all, human diseases have a preclinical, a prodromal, and a clinical stage.