The serotonin 5-HT6 receptor represents a novel pharmacological target whose impact on physiopathology of CNS functions remains undetermined. Some receptor antagonists have been synthesized and they show a modulatory role in learning and memory processes and food intake. The pharmacology of 5-HT6 receptor agonists is still under evaluation. However, both 5-HT6 antagonists and agonists seem to exert potential antidepressant activity. Recently, a second messenger system has been discovered. 5-HT6 receptor function is becoming more and more intriguing. Thus, the aim of the present book is to try to clarify the pharmacology of 5-HT6 receptors.