Biological regeneration, a fundamental capacity of all living things, includes processes ranging from the constitutive turnover of cellular components to the extraordinary ability of bisected hydra to become two structurally complete individuals or of salamanders to replace amputated limbs and tails. While historical debate over the nature of regeneration relied largely on its superficial similarity to embryonic development, advances in molecular biology and developmental genetics have now demonstrated a striking concordance between development and regeneration that reaches across phyla.