Estrogen is a hormone critical in the development, normal physiology and pathophysiology1 of numerous human tissues2. The effects of estrogen have traditionally been solely ascribed to estrogen receptor α (ERα) and more recently ERβ, members of the soluble, nuclear ligand–activated family of transcription factors3. We have recently shown that the seven-transmembrane G protein–coupled receptor GPR30 binds estrogen with high affinity and resides in the endoplasmic reticulum, where it activates multiple intracellular signaling pathways4. To differentiate between the functions of ERα or ERβ and GPR30, we used a combination of virtual and biomolecular screening to isolate compounds that selectively bind to GPR30. Here we describe the identification of the first GPR30-specific agonist, G-1 (1), capable of activating GPR30 in a complex environment of classical and new estrogen receptors. The development of compounds specific to estrogen receptor family members provides the opportunity to increase our understanding of these receptors and their contribution to estrogen biology.