Recent genetic data from patients with Huntington’s disease (HD) show that DNA repair is an important factor that determines how early or late the disease occurs in individuals who carry the expanded CAG repeat in the HTT gene that causes HD. The processes of DNA repair further expand the CAG repeats in HTT in the brain implicated in pathogenesis and disease progression. This special issue of the Journal of Huntington’s Disease (JHD) is a compendium of new reviews on topics ranging from the discovery of somatic CAG repeat expansion in HD, to our current understanding of the molecular mechanisms involved and the development of potential new therapies targeting these mechanisms.