Regeneration is a fundamental attribute of all living things, whether it be simple tissue restoration or the complete replacement of lost body parts such as limbs, tails or even heads. As a biological problem, it began to be formally studied over 250 years ago in crustaceans by René-Antoine Ferchault de Réaumur (1683-1757), and soon after in hydra by Abraham Trembley (1710-1784). In the years to come, regeneration attracted the attention of prominent biologists such as Charles Darwin (1809-1882) and Thomas Hunt Morgan (1866-1945). A long-standing problem of biology, regeneration in metazoans still awaits a satisfactory mechanistic explanation. Our laboratory's goal is to identify and to study the molecular components underpinning this phenomenon. We are approaching this problem by analyzing and manipulating the regenerative properties of an invertebrate organism, chiefly the freshwater planarian Schmidtea mediterranea.