Alzheimer's disease, the commonest cause of dementia, is a growing global health concern with huge implications for individuals and society. In this review, current understanding of the epidemiology, genetics, pathology and pathogenesis of Alzheimer's disease is outlined, before its clinical presentation and current treatment strategies are discussed. Finally, the review discusses how our enhanced understanding of Alzheimer pathogenesis, including the recognition of a protracted preclinical phase, is informing new therapeutic strategies with the aim of moving from treatment to prevention.