Genetic strategies to elucidate the substrates for memory induction, maintenance, and retrieval have evolved rapidly during the previous decade. Here we review the wealth of information that has been derived from work with “transgenic” mammals, and attempt to establish a framework from which we might better appreciate the genetic and molecular constituents of “normal” learning and memory, as well as of common dementias (e.g., Alzheimer's disease) that impinge on these processes. From this body of work, we are poised to construct comprehensive descriptions of the mechanisms that subserve memory storage in the brain, and moreover, to envisage practical strategies to overcome certain learning deficits and to modulate learning in otherwise normal individuals.