The hematologic disorders of beta-thalassemia and sickle cell disease are the most prevalent of human genetic diseases. Although palliative therapies and curative stem cell transplantation therapy have been developed for these disorders, treatment still remains suboptimal and many patients suffer significant morbidity and early mortality. Therefore, development of a gene therapy approach has been sought for many years. Major progress in the globin gene therapy field has been achieved by several laboratories. Using lentiviral vectors to obtain high-level expression of complex globin gene cassettes, therapeutic correction of several murine models of beta-thalassemia, and sickle cell disease was recently reported. This progress, coupled with developments in the ability to select and expand genetically modified stem cells in vivo, has advanced the possibility of gene therapy for the hemoglobin disorders in the near future. We review the developments in several areas that are critical for successful gene therapy of the hemoglobin disorders.