Dopamine is the predominant catecholamine neurotransmitter in the brain, where it controls numerous functions. The physiological actions of dopamine are mediated by five G protein-coupled receptors (GPCRs). The D2 dopamine receptor (D2DR) is the model receptor of D2-like subfamily of dopamine receptors and is prototypic of GPCRs that inhibit adenylyl cyclase and activate K+ channels.Taken together, these studies represent a significant characterization of both the function and structure of D2DR oligomerization. The realization that oligomerization is a pivotal aspect of GPCR biology with implications for trafficking, signalling, and pharmacology has provided more intricate models for understanding the physiological roles of these receptors and prompted a re-evaluation of established ideas. The determinations for D2DR oligomers in this study may yield clues to the principles governing the oligomerization of all rhodopsin-like GPCRs and thereby a better understanding of these important proteins.Initial biochemical characterization of D2DR dimerization revealed that there was a robust interaction between receptor monomers that could not be dissociated by chaotropic agents. Further, neither agonist nor antagonist binding to the D2DR affected the extent of receptor dimerization. Interestingly, co-expression of the wild-type D2DR with truncation mutants and some point mutants of the D2DR resulted in inhibition of cell surface expression of the receptor as the result of an interaction between the receptor mutant and the D2DR. This finding suggested that oligomerization of the receptor occurred prior to cell surface trafficking and that a properly arranged oligomeric complex was required for D2DR trafficking. An investigation of the structural assembly of dimeric receptors showed that there are several sites of interaction including transmembrane domain interactions. Specifically, a symmetrical transmembrane domain 4 interface was identified as being one of these sites.Until recently, it has been assumed that GPCRs function as monomers. However, it has become well established that GPCRs can form dimers and oligomers, leading to a re-evaluation of the mechanisms thought to mediate GPCR function. This thesis documents the characterization of the functional role of D2DR homo-oligomers and elucidation of the sites of intermolecular association in D2DR homodimers. It includes experiments performed prior to the first widely accepted published reports on GPCR dimerization and during the explosive period of research when theories concerning oligomerization evolved rapidly.