Chapter 5 provides an overview of the evolutionary history of the globin gene superfamily and places the evolution of vertebrate-specific globins in phylogenetic context. The duplication and functional divergence of globin genes has promoted key physiological innovations in respiratory gas transport and other physiological functions during animal evolution. A combination of both tandem gene duplication and whole-genome duplication contributed to the diversification of vertebrate globins. Phylogenetic reconstructions arrange vertebrate globins into those that derive from vertebrate-specific duplications (cytoglobin, globin E, globin Y, and the independently derived myoglobin-like and hemoglobin-like genes of jawed vertebrates and jawless fishes [lampreys and hagfish]) and those that derive from far more ancient duplication events that predate the divergence between deuterostomes and protostomes (androglobin, globin X, and neuroglobin). Tracing the evolutionary history of deuterostome globins reveals evidence for the repeated culling of ancestral diversity, followed by lineage-specific diversification of surviving gene lineages via repeated rounds of duplication and divergence.