Nano product registries in Europe are the newest twist to satiating the public’s relentless “right to know.” Nominally intended to prevent hazards, facilitate monitoring, and promote consumer choice, nano product registries also risk stigmatizing nano products, diverting limited government and private resources, and potentially creating commercial barriers to a promising technology. This article in the American Bar Association’s Natural Resources & Environment magazine focuses on efforts of multiple European countries that are presently at varying stages of establishing product registries to keep track of nanomaterials and the products that contain them. After outlining the stated purposes of these registries and explaining how they operate, the article explores whether they are achieving their stated goals or inadvertently inviting unintended consequences.