X-ray crystallography was used to solve the atomic structure of the ligand binding domain of the metabotropic glutamate receptor type1 homo-dimer, making it possible to show the conformational change of this domain upon glutamate binding. Studies of dimeric metabotropic receptors thereafter have focused on the respective roles and interaction of the two subunits, on the activation mechanisms following the structural rearrangements of the ligand-binding domain, and on the functional significance of polyvalent cations, the binding of which was identified in the crystal. The direct interaction between the GABA(B) receptor and the metabotropic glutamate receptor (mGluR1) has also attracted attention. Recently, attention has focused on incorporating these structural features into a functional view of the receptors.