Serotonin is a multifunctional signaling molecule that plays extra-cerebral roles, not only in adult life, but in development as well. Although, research concerning extracerebral serotonin is growing rapidly and interest in the subject is great, neither the physiological control and the underlying molecular processes, nor the involvement of peripheral serotonin in disease, have definitively been established. The role of serotonin in peripheral tissues, furthermore, has been neglected and under-represented at current meetings, which have focused on the 3-5% of the body’s serotonin that is present in the central nervous system. Therefore, this Keystone Symposia meeting aims to reveal insights into the role of serotonin in peripheral tissues, specifically in the diagnosis, prevention and treatment of many diseases, which is long overdue.