Publisher Summary This chapter focuses on the role of dopamine receptors in neurotransmission, their structures, and their functions. Dopamine (DA) is one of the major monoamine neurotransmitters in the mammalian brain. It is generated by hydroxylation and decarboxylation of the amino acid tyrosine, and further metabolized into epinephrine and norepinephrine. Dopamine receptors belong to the superfamily of GPCRs and are all considered to be in the Rhodopsin-like Class A family of 7-transmembrane receptors based on sequence homology and function. For all the five DARs the N-terminus and extracellular loops are glycosylated and cysteine residues between the loops form disulfide bonds. Higher order GPCR signaling structures have long been hypothesized to exist, however there remains some controversy over the biological significance of such structures. The significance of arrestin dependent signaling for GPCRs may be manifold. First, arrestin dependent signaling is usually more persistent than G protein signaling. Second, it has been shown that for certain GPCRs a given compound can act as an agonist at one signaling pathway and an antagonist at the other or vice versa.