In recent years political, religious, and scientific communities have waged an ethical debate regarding the development and research of embryonic stem cells. On the one hand, does the manipulation of embryonic stem cells destroy human life? On the other hand, do limitations imposed on stem cell research harm the patients who might otherwise benefit? John Lynch’s “What Are Stem Cells? Definitions at the Intersection of Science and Politics,” having identified this moral stalemate between the rights of the embryo and the rights of the patient, utilizes it as the framework for a larger discussion about the role of definitions as key elements of rhetorical strategy. In the case of stem cells, the controversy arises from the manner in which stem cells are defined-in particular, whether they are defined with an appeal to their original source, or else to their future application. Definitions such as these, Lynch argues, are far more than convenient expository references; they function to determine the realities of any given social discourse. The book addresses definitions conceptually-their stability in the face of continuous technological innovation, their versatility at the crossroads of scientific and public forums, and their translations and retranslations through politics. Most importantly, it recognizes definitions as central issues, not only within the topic of stem cell research, but in all argumentation.