Unambiguous definition of nanomaterials is of fundamental importance for intended regulations on nanomaterials, since not only the legal obligations have to be clear, but also just what is subject to them. For this purpose it is necessary, among other things, to enhance such definitions.  Nanomaterials such as agglomerates and aggregates should also be defined, since besides the size of nanomaterials their specific surface and boundary layer properties are also important  for risk assessment.