Social anxiety disorder (SAD) also know as social phobia is increasingly recognized as a highly prevalent and disabling psychiatric disorder. SAD patients demonstrate cognitive-affective distortions in relation to social situations and abnormal activation patterns in limbic structures during functional imaging. Behavioral inhibition is an endophenotype that may be useful in understanding vulnerability to SAD, and that has specific imaging and genetic correlates. From an evolutionary perspective, it has been speculated that SAD represents a false appeasement alarm. It is notable that SAD responds to selective serotonin reuptake inhibitors and monoamine oxidase inhibitors, but not to most tricyclic antidepressants; this finding is consistent with the importance of serotonin and dopamine in mediating this disorder.