It seems hard to believe that Dolly the cloned sheep was born 10 years ago, kindling furious arguments over the prospects and ethics of cloning a human. Today, the controversy over cloning is entwined, often confused, with concerns over the use of human embryonic stem cells. Most people are unclear what cloning is, and they know even less when it comes to stem cells. In teaching, it can be engaging to lead with a controversy or to start with the medical promise of a given research topic. For stem cells, however, it is important to impress upon students the essential role of stem cells in the natural processes of development and regeneration before getting into potential medical benefits, let alone controversies. This article focuses on stem cells: What are they? What aren't they? and What are the ethical issues that students should consider? (Contains 7 figures.)