Accumulating evidence has confirmed the existence and functional significance of GPCR and other types of receptor homodimers and heterodimers. However, many aspects of the biology and pharmacology of the dimerization process remain unclear. Several crystal structures of the dimerized proteins or protein-ligand complex have provided useful insights to the understanding of such process. As a common phenomenon of most receptors, homodimerization and heterodimerization have added a new dimension to characterize the receptor different from the traditional way, and open a new avenue to rational drug design and discovery.