Huntington's disease (HD) is a progressive, fatal, dominant inherited neurodegenerative disorder caused by an unstable expansion of CAG repeats within the coding region of the IT15 gene that encodes for a protein called huntingtin (htt). The clinical hallmark of HD is a severe motor impairment, but cognitive and psychiatric symptoms are early clinical features in HD that often appear before the onset of motor signs. This book discusses the prevalence, pathogenesis and treatment of HD.