||This MODENA COST action is supported by COST, an intergovernmental framework for European Cooperation in Science and Technology, which allows the coordination of nationally-funded research on a European level. The following agencies coordinate the COST initiative. Nanotechnology produces engineered nanomaterials (ENM) having new or enhanced physico-chemical properties in comparison to their micron-sized counterparts. Some of these properties, like the high surface area to volume ratio, make them potentially dangerous to humans as shown by research in NANOTOXICOLOGY. To promote the development of a new generation of ENM that are SAFE-by-DESIGN, an understanding of the relationship between the ENM STRUCTURE and biological ACTIVITY is needed. In this context the Quantitative Nanostructure-Toxicity Relationships (QNTR) computational modelling technique is an effective alternative to experimental testing since it enables the prediction of (eco)-toxicological effects based on ENM structure only.