Estrogen is an important hormone in human physiology. It acts both via transcriptional regulation as well as via modulation of intracellular signaling through second messengers. Although estrogen's transcriptional effects occur through classical nuclear steroid receptors (ERs), recent studies reveal the existence of a novel 7-transmembrane G protein-coupled receptor, GPR30, which responds to estrogen and tamoxifen stimulation with rapid cellular signaling including ERK activation, PI3K activation, calcium mobilization and cAMP production. To distinguish between ER- and GPR30-mediated signaling, we have identified a novel GPR30 agonist that exhibits high specificity for GPR30. In this review, we will describe recent work to further our understanding of the role of GPR30 in estrogen biology.