In the twelve years since the molecular elucidation of the metabotropic glutamate receptor subtype 1, a class III family of G-protein-coupled receptors has emerged; members of this family include the calcium-sensing receptor, the GABA(B) receptor, some odorant receptors and some taste receptors. Atomic structures of the ligand-binding core of the original metabotropic glutamate receptor 1 obtained using X-ray crystallography provide a foundation for determining the initial receptor activation of this important family of G-protein-coupled receptors.