Cnidarians – the animal phylum that includes sea anemones, corals, jellyfish, and hydra – occupy a critical position in the tree of life. As the simplest Eumetazoans (animals with a tissue grade of organization) they are the most primitive animals with epithelial cells, neurons, stem cells, complex extra-cellular matrix, muscle fibers, and a fixed axis of symmetry. Ediacaran fossils with Cnidarian affinities are among the most ancient animal relics. As the principal architects and components of coral reefs, anthozoans (corals) are responsible for the maintenance of tremendous marine diversity. The sea anemone Nematostella vectensis, a member of the basal class Anthozoa within the Cnidaria, is emerging a model system for the molecular dissection of Cnidarian development, providing key “evo-devo” studies to elucidate the emergence, elaboration, and deployment of the basic complement of genes that underlie the formation of animal body plans. To illuminate the evolutionary origins of animals we have sequenced the genome of Nematostella.