The politics of stem cell research poses a puzzle: the explanation of different national responses to the same scientific breakthroughs. Policy struggles across the major scientific powers have revolved around similar values—the protection of human life and solidarity with the sick—but generated very different regulatory outcomes. Bringing in historical and institutional legacies can shed light on those differences. The article develops an analytical framework around the path-dependent effects of state institutions on value-driven issues and applies it to the politics of stem cell research in the United Kingdom and Germany. Historical institutionalism, it argues, can be extended beyond the study of political economy and the welfare state to issues marked by sharp value conflict.