Bioethics--the study of ethical issues in science and medicine--has grown to become a significant academic and service-oriented discipline with its own research centers, conferences, journals, and degree programs. As these issues have moved to the center of public debate, the law has assumed an increasingly important place in the discipline of bioethics. Today, embryonic stem cell research stands out as a critically important issue about which the U.S. has neither ethical consensus nor clear, comprehensive regulation. The ethical debate centers on the fact that stem cell research involves the destruction of very early human embryos. This article provides a brief scientific background followed by a discussion of key ethical and legal/regulatory issues that surround embryonic stem cell research.