This article addresses the relationship between scientific expertise and policy in European chemicals regulation. We argue that the role of scientific expertise in the European regulation of chemicals varies across decision-making levels, countries, and stages of the policy process. Our case study of the role of scientific expertise in the regulation of brominated flame retardants illustrates considerably different manifestations of this interconnected process across regulatory arenas, even though this case concerns a single group of substances. On the European Union level, we find a mix of technocracy and politicization; in Sweden, a clear-cut politicization; and in Poland, noninvolvement. Such differences can be explained by a combination of factors, in particular frame dominance, and mobilization of advocacy coalitions.