Several genes that influence susceptibility to Alzheimer's disease (AD) have been known for over two decades. Recent advances have elucidated novel candidate genes and the pathogenetic mechanisms underlying neurodegeneration in AD. Here, we summarize what we have learned from studies of the known AD genes with regard to the causes of AD and emerging therapies. We also review key recent discoveries that have enhanced our understanding of the etiology and pathogenesis of this devastating disease, based on new investigations into the genes and molecular mechanisms underlying AD.