Nanomaterials and nanotechnology are widely used today, but their use may expose humans and the environment to new health and sustainability risks. In order to control and minimise these risks, the EC has mandated European standardisation bodies to develop standardised methods that can reliably characterise manufactured nanomaterials. Nanoparticle size is one of the parameters that characterises nanoparticulate materials. This project will develop methods, reference materials and modelling to improve the traceability chain, comparability and compatibility of nanoparticle size measurements to support standardisation. The project will contribute to both new standards documents and those under development with improved measurement procedures to accurately measure the size and size distribution of nanoparticles based on modelling and new reference nanoparticles. Depending on the particular sizing method used, these activities will take place within the framework of CEN/TC 352 “Nanotechnologies”, ISO/TC 229 ‘Nanotechnologies’, ISO/TC 24/SC 4 ‘Particle characterization’ and ISO/TC 201/SC 9 ‘Scanning probe microscopy’.