Tic disorders which involve sudden and repetitive movements, gestures, or vocalizations form a spectrum ranging from simple transient tic disorders to more severe tic disorders that may cause significant impairment in psychosocial development, self esteem, family and social relationships, or academic/career performance. Around 6-20% of children experience simple transient tic disorder, while the prevalence of Tourette Syndrome (TS), a more severe tic disorder, is 5 to 6 cases in 1000 children. The severity and frequency of tics may change over time: usually peaking at the beginning of the second decade of life and diminishing towards the end of puberty. Psychosocial stressors, genetic and epigenetic factors and the interactions between these factors are involved in the etiology of tic disorders. In recent years, with the understanding of the suitability of TS as a model in investigating the interaction between genetic and environmental risk factors, increasing number of researches have been conducted in that direction.