The past 25 years have seen enormous progress in the deciphering of the genetic and molecular basis of ataxias resulting in an improved understanding of their pathogenesis. The most significant milestones during this period were the cloning of the genes associated with the common spinocerebellar ataxias (SCAs), ataxia telangiectasia (AT) and Friedreich ataxia (FRDA). To date, the causative mutations of more than 30 SCAs and 20 recessive ataxias have been identified. In addition, there are numerous acquired ataxias with defined molecular causes so that the entire number of distinct ataxia disorders exceeds 50 and possibly approaches 100. Despite this enormous heterogeneity, a few recurrent pathopyhsiological themes stand out. These include protein aggregation, failure of protein homoestasis, perturbations in ion channel function, defects in DNA repair and mitochondrial dysfunction. The clinical phenotypes of the most common ataxia disorders have been firmly established, and their natural history is being studied in ongoing large observational trials. Effective therapies for ataxias are still lacking. However, novel drug targets are under investigation, and it is expected that there will be an increasing number of therapeutic trials in ataxia.