Leukodystrophies are heritable disorders primarily affecting the white matter of the central nervous system. They are clinically characterized by spasticity, optic atrophy, and ataxia. These are a heterogeneous group of disorders, including hypomyelinating disorders and demyelinating disorders due to abnormal accumulations. Although individually rare, together they are responsible for substantial disease burden. Essentially all these disorders have infantile, juvenile, and adult presentations. Understanding the genetic and biochemical bases of these disorders opens the door to therapeutic approaches.