Inspired by biological systems, artificial composite materials nowadays may be micro-tailored with a hierarchical structure, or may be produced with sculptured chiral structures, or with stabilized negative-stiffness inclusions. The result is that these new materials can achieve surprisingly excellent mechanical properties.The technological application of these new high-performance composite materials is limited by fracture nucleation and propagation at nano and micro scales. In fact it is very difficult to simultaneously achieve high values of strength and toughness, for which ordinarily there is a trade-off. The aim of this project is the development of new models of fracture mechanics for innovative composite materials, bridging together the different length-scales and thus overcoming the main limitations of linear fracture mechanics (LEFM). In fact, since LEFM is a scale-free theory, it is unable to characterize materials with microstructure and to describe size-effects at small scales.The goal will be achieved by a novel multiscale approach to fracture mechanics combining continuum and discrete modelling. In particular, at the microscale the heterogeneous microstructure of the composite material will be described as a continuum micropolar medium incorporating appropriate length-scales, thus capable of capturing size-effects. At the nanoscale the discrete structure of the material will be described in terms of lattice models in order to understand the mechanism of dissipation and the properties of waves generated by propagating cracks. The continuum and discrete modelling will be combined through the concept of structural interface, where a discrete structure representing the interface of finite thickness is embedded in a continuum body.These models will have an impact on the design of new artificial composite materials which combine high strength with uncompromised toughness properties.