Ample evidence has demonstrated that sex steroid hormones, such as the potent estrogen 17ß-estradiol (E[subscript 2]), affect hippocampal morphology, plasticity, and memory in male and female rodents. Yet relatively few investigators who work with male subjects consider the effects of these hormones on learning and memory. This review describes the effects of E[subscript 2] on hippocampal spinogenesis, neurogenesis, physiology, and memory, with particular attention paid to the effects of E[subscript 2] in male rodents. The estrogen receptors, cell-signaling pathways, and epigenetic processes necessary for E[subscript 2] to enhance memory in female rodents are also discussed in detail. Finally, practical considerations for working with female rodents are described for those investigators thinking of adding females to their experimental designs.