Leukodystrophy is a common central nervous system manifestation of inborn errors of metabolism. Until magnetic resonance imaging (MRI) emerged as a clinical tool, the diagnosis of leukodystrophy was difficult and imprecise; MRI has allowed new understandings and classifications of leukodystrophies that have greatly enhanced both our diagnostic ability and our understanding of these complex disorders. However, optimal use of MRI in this setting requires a fundamental understanding of myelin structure, myelin development, and the changes seen on MRI with myelination and demyelination. The purpose of this review is to provide the reader with the necessary tools for the use of MRI to diagnose and follow patients with leukodystrophies.