Book excerpt: Serotonin (5-hydroxytryptamine, often cited as 5-HT) is one of the major excitatory neurotransmitters, and the serotonergic system is one of the best studied and understood transmitter systems. It is crucially involved in the organization of virtually all behaviours and in the regulation of emotion and mood, and pathological alterations in the serotonergic system underlie behaviour and psychiatric conditions (among a host of very successful drugs targeting the serotoninergic system are Prozac and Zoloft). This is the first truly integrated handbook providing a broad overview over the many face