Leukodystrophies are serious, progressive, genetic disorders of CNS myelin. They may result from abnormalities of the oligodendrocyte or any of the other of myriad of supporting cells or tissues. With recent developments in neuroimaging, their presence is becoming increasingly noted even in situations where they were not suspected. More importantly, new genetic tools have improved our ability to diagnose. An understanding of pathogenesis is still evolving, but it is expected that this will assist in developing targeted therapies for these devastating disorders.