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Sequestration of G protein-coupled receptors from the cell surface is a commonly observed phenomenon following agonist-stimulation. This process is now believed to be important for receptor resensitization as well as for signal transduction. Over the years, numerous studies have aimed at understanding the molecular mechanisms underlying internalization. Proteins such as the G protein-coupled receptor kinases (GRKs) and the ß-arrestins, which were initially characterized as desensitizing molecules, have been shown to be important regulators of the endocytic process. Recently, numerous interacting partners have been identified for each of these two classes of proteins. However, the details regarding the sequence of these interactions and the cross-talk between signaling pathways containing the different protein complexes are just beginning to be uncovered. In this review, we summarize these findings and discuss the role of GRKs and ß-arrestins, two families of key regulatory proteins that regulate G protein-coupled receptor endocytosis. [Copyright &y& Elsevier]