Effective electronic structure methods based on density functional theory and multiscale modeling to address large scale systems in condensed matter. In this context, we develop approaches for the simulation of complex interface systems, including metallic surfaces and liquid phases. Sometime we rely on the hybrid quantum mechanics/molecular mechanics (QM/MM) formalism, also augmented with polarization effects, e.g. image charges and variable charges. Another possible strategy is to exploit the locality properties of subsystems, solving the electronic structure problem for the individual fragments, and correct with some adequately defined embedding potential. Schemes of this type, which are better suited for the study of molecular liquids, mixtures, and solutions, can be further developed to address also several molecular properties.