The polybrominated diphenyl ethers (PBDEs) are a class of brominated flame retardants used extensively in an array of textiles and plastics. Initially viewed as inert and nontoxic, in recent years an emerging body of science has cast doubt on this perception. Consequently, the compounds have drawn sustained government, media, and lobby group focus in the United States and Europe, yet have taken contrasting trajectories in different risk regulation regimes. We present a longitudinal analysis of these pathways, examining the actions of legislatures, executives, courts, scientists, and pressure groups. We show that the emergence and resolution of PBDEs as a risk issue was strongly shaped by path dependency, political entrainment (inter-institutional conflict unrelated to PBDEs), and partisan lawmaking. This raises the question of whether risk-based principles are capable of being the foundation on which managing the potential for harm can be based—even when that harm is associated with specific objects like flame-retardant chemicals. We conclude by reflecting on the difficult normative issues that are raised.