Serotonin 5-HT2A receptors are essential for a large number of physiological functions in the central nervous system and periphery. This review article summarizes our current knowledge of the molecular biology and mechanisms of regulation of 5-HT2A receptors. The mode of drug binding using data derived from molecular modeling and site-directed mutagenesis is described. The cellular and subcellular localization of 5-HT2A receptors is described, and the concentration of 5-HT2A receptors on apical dendrites of pyramidal neurons is emphasized. Various modes of regulation of 5-HT2A receptors are also summarized, including transcriptional, post-translational and mRNA editing processes. Finally, an integrated model of 5-HT2A receptor regulation that involves various protein kinases (protein kinase C, G-protein receptor kinases), arrestins, clathrin-coated vesicles, endosomes and lysosomes. The relevance of these pathways for antidepressant and antipsychotic drug actions is emphasized.