Dr. Kiessling points out the need to resolve the confusion that has crept into the scholarly and legal discussion of embryos. 1 We agree. In our judgment, however, the solution is not to coin new terms, such as" preembryo" or" ovasome," 2 or redefine existing terms, thus repeating past errors. The solution lies, instead, in education and the démystification of early stages of embryogenesis so that societal concerns can be addressed openly and without artifice. What is an embryo? Historically, this is a simple question with an equally simple answer: An embryo is the product of the successful union of sperm and egg. In biological terms, the creation of an embryo marks the beginning of life. An embryo has the unique property that it has some measurable potential to progress down a path of development, becoming, in the best cases, a fully formed individual of the same type that produced the sperm and egg from which it arose. This contrasts with the normal fate of either sperm or egg in the absence of fertilization; both cell types are destined to die without further development. New technologies require us to expand the historical definition of an embryo to include those cases in which delivery of the embryo's genetic material is not via sperm and egg (eg," cloning" by adult cell nuclear transfer, as well as techniques used to create embryos that have only maternal or only paternal genetic material). In the case of cloned mammalian embryos, a complete set of chromosomes is delivered to the egg by the transfer of a somatic cell nucleus. However, the method by which the genetic material and the ooplasm are brought together to create the embryo does not alter the nature of the final product of that union. The composi-