Bridging the gap between electronic and atomistic levels plays a crucial role in multi-scale modelling of mechanical behaviour of materials. In this review, we summarise a methodology for linking systematically these two levels starting from the first-principles density functional theory and proceeding via the screened tight-binding approximation to development of reliable and transferable many-body interatomic bond-order potentials. We focus our investigations on material properties related to the electron-to-atom ratio. An immediate area of application is studies of the structure and properties of crystal defects in transition metals and intermetallic compounds based on transition metals, where the mixed character of covalent and metallic bonds represents a very challenging issue for understanding mechanical properties at the engineering scale. The need for environmental dependence of bond-order potentials as well as the implication of screening effects on bonding properties of alloys are discussed in connection with modelling of the core structure of dislocations in materials with negative Cauchy pressures and in body-centered cubic (bcc) transition metals. The latter are prime candidates as fusion power-plant materials. We discuss our current work on multiscale modelling, the behaviour of bcc materials under high-energy neutron irradiation, and emphasize the importance of quantum-mechanics in constructing reliable interatomic potentials for large scale molecular dynamic simulations. (C) 2006 Elsevier Ltd. All rights reserved.