In order to regulate nanomaterials and to determine mandatory product labelling a generally accepted agreement what the term “nanomaterial” means has to be reached beforehand. The EU Parliament requires that a definition shall be science-based and comprehensive. Furthermore, for regulatory measures in individual sectors, it shall be unambiguous, flexible, easy and practical to handle. During the past few years various institutions came up with suggestions for a definition, leading to a recommendation of the EU commission, which finally is being accepted into new and existing EU legislation. Some provisions in this proposal are controversial and the implementation into specific sectoral legislation constitutes a major challenge.