Huntington's disease is caused by an abnormal CAG expansion within the gene encoding Huntingtin which induces a major cortico-striatal degeneration as well as motor and cognitive impairments. Since the discovery of the present mutation, a number of experimental data have been collected to uncover the physiopathological consequences of mutated Huntingtin expression. Here, we review the molecular and cellular mechanisms underlying and show how this better knowledge can be translate to clinical trials in patients.