Although highly controversial just a few years ago, the idea that G-protein-coupled receptors (GPCRs) may undergo homo-oligomerization or hetero-oligomerization has recently gained considerable attention. The recognition that GPCRs may exhibit either dimeric or oligomeric structures is based on a number of different biochemical and biophysical approaches. Although much effort has been spent to demonstrate the mechanism(s) by which GPCRs interact with each other, the physiological relevance of this phenomenon remains elusive. An additional source of uncertainty stems from the realization that homo-oligomerization and hetero-oligomerization of GPCRs may affect receptor binding and activity in different ways, depending on the type of interacting receptors. In this brief review, the functional and pharmacological effects of the hetero-oligomerization of GPCR on binding and cell signaling are critically analyzed.