Publisher Summary This chapter summarizes the current knowledge about the structure–function relationships of the globin gene system as derived from studies at the level of DNA and RNA. It discusses some of the sequence comparisons that relate to the evolution of this gene system and reviews the status of the applications of this molecular genetic knowledge to the understanding of the human hemoglobinopathies. The bulk of literatureon globin precludes anything approaching exhaustive coverage. Hemoglobin is a metalloprotein tetramer consisting of two α-like globin polypeptides and two β-like globin chains. The striking achievements of the past five years has been the rapid definition at the DNA level of the heterogeneous collection of mutations that lead to α- and β-thalassemia, which have themselves provided crucial information about the control of gene expression in vivo. The recognition of linked polymorphisms, the development of mutation-specific oligonucleotide probes, and the possibility of first-trimester chrionic villus biopsy have made the prenatal diagnosis of sickle-cell anemia and β-thalassemias of immediate applicability, and appropriate resources must be marshaled to offer this technology to the areas of the world where it is most needed.