Publisher Summary This chapter discusses the structure and function of thrombin receptor and their biological roles of the cloned thrombin receptor. The thrombin receptor's deduced amino acid sequence revealed it to be a member of the seven transmembrane domain receptor family. Its primary sequence is most closely related to the receptors for neuropeptides, glycoprotein hormones, and proinflammatory mediators such as C5a and IL8. The receptor sequence reveals five consensus N-linked glycosylation sites in regions predicted to be extracellular. Recent unpublished studies from our group demonstrated that the thrombin receptor is rapidly phosphorylated upon activation, probably as part of the mechanisms for terminating receptor signaling. Mapping of specific phosphorylation sites remains to be accomplished. Synthetic peptides mimicking the thrombin receptor's agonist peptide domain and the receptor cDNA itself have provided new tools for defining the role of the cloned receptor both in intracellular signaling events and in various thrombin-induced cellular functions. For the purpose of this chapter, discussion of the thrombin receptor's role in cellular events will be largely confined to platelets.