Tourette's syndrome (TS) is an inheritable, childhood-onset neuropsychiatric disorder characterized by the presence of motor and phonic tics. Despite decades of extensive studies, the exact disease etiology remains poorly understood. It is believed that susceptibility to TS is determined by the interactions of multiple genetic loci with unknown environmental factors. As a result, a great deal of research has been focused on identifying TS susceptibility genes. Thus far, at least 12 susceptibility loci have been suggested by genome-wide screenings, but none of them has been replicated probably due to genetic heterogeneity. Candidate gene approach has also suggested evidence for several genes relevant to neuronal signaling such as dopamine receptor and serotonin receptor. This book discusses the current state of genetic studies in TS susceptibility.