It is rarely a compliment to be accused of "politicizing science." But the term itself has at least two meanings-one negative and one positive: The first meaning involves distorting scientific facts or scientific evidence to promote one's own ideology or agenda. The temptation to engage in such a practice exists (and sometimes prevails) on all sides of the political spectrum: environmental activists tempted to exaggerate the threat of global warming; industry advocates tempted to downplay the ecological effects of oil exploration; pro-life activists tempted to over-hype the promise of adult stem cells; embryo research advocates tempted to promise cures for dreaded diseases based only on preliminary animal experiments. Such "politicization" is rightly condemned by responsible people on all sides. The second meaning of "politicizing science," however, is not a problem but a necessity. Politics, rightly understood, is the activity of ordering our life together, and insofar as science both affects and depends on civic life, it is rightly a political issue. Indeed, all democratic societies need to debate the relative importance of different scientific projects (e.g., curing AIDS vs. going to Mars), the relative risks and benefits of certain areas of scientific research (e.g., creating artificial viruses), or the ethical dilemmas of proceeding or not proceeding with certain types of experiments (e.g., embryonic stem cells). Science alone cannot answer the types of questions that science sets before us, and a self-governing people must govern the direction of science, especially (but not only) when citizens are paying the bills. The challenge, therefore, is to avoid politicizing scientific facts while engaging in political debates about science. This challenge is made even greater by the complexities and uncertainties that are intrinsic to most areas of advanced science. After all, we do not know the scientific truth while we are looking for it; the very need for "research" suggests the reality of uncertainty; and the history of science is filled with examples of scientific "common sense" being turned on its head. The scientific facts are sometimes hazy not because of willful distortion but because of honest disagreement. And so it is not only citizens and statesman who argue about the role of science in society, but the scientists themselves who argue about what is true, what will work, and what is most important in their own scientific fields. These two debates take place side by side, sometimes informing and sometimes deforming one another. Since the late 1990s, the debate over embryonic stem cell research has been central to this larger debate about science and American democracy. The debate has been very polemical at times-with research advocates claiming the mantle of Galileo in demanding more federal funding and fewer regulations, and research opponents claiming that embryo research will lead America toward a "brave new world" or "culture of death" (McDermott, 2001; Connor, 2001). On balance, however, the stem cell debate has been an impressive and important one. It is rare that America discusses such deep questions in such a serious way-questions about human nature, human origins, the aspirations of medical research, and the character of the good society. This is, in the deepest sense, what the stem cell debate is all about. We are discussing the smallest human thing-the human embryo-which sets before us the biggest human questions (Cohen, 2003a). And by studying the character of this particular debate, one can discern many of the deeper dilemmas that lie at the crossroads between modern science and modern democracy. I will discuss three things: First, I'll try to explain briefly how embryonic stem cells became an issue of great public importance, and how it burst into national consciousness in 2001. second, I'll explore why this debate is uniquely important to the future of American life and American politics, and especially to the meaning of our own most cherished ideals. …