Serotonin (5-HT) receptors are part of the G protein-coupled and ligand-gated ion channel families. 5-HT exerts its diverse actions by binding to cell surface receptors which can be classified into seven distinct families (5-HT1 to 5-HT7) according to their structural diversity and mode of action. Some of the 5-HT families are comprised of multiple receptors which share similar structural and mechanistic properties but display very different operational profiles. Evidence continues to mount in support of the important roles of the 5-HT receptors in various neuropsychiatric disorders such as anxiety, depression, schizophrenia, migraine and drug addiction. The 5-HT receptors may also play an important role in obesity, aggression, sexual behaviour and cardiovascular disorders. A number of selective/non-selective 5-HT agonist and antagonist ligands (drugs) have been developed to challenge many of these disease states.