Embryonic stem cell research is morally and politically controversial because the process of deriving the embryonic stem cells kills embryos. If embryos are, as some would claim, human beings like you and me, then ES cell research is clearly impermissible. If, on the other hand, the blastocysts from which embryonic stem cells are derived are not yet human beings, but rather microscopic balls of undifferentiated cells, as others maintain, then ES cell research is probably morally permissible. Whether the research can (...) be justified depends on such issues as its cost, chance of success, and numbers likely to benefit. But this is an issue for any research project, not just ES cell research. What makes the debate over ES cell research controversial is that it, like the debate over abortion, raises “questions that politicians cannot settle: when does human life begin, and what is the moral status of the human embryo?” This paper looks at several theories of moral status and their implications for embryo research. (shrink)