The focus of our research is on the development of theoretical and computational approaches targeting the electronic structure of extended systems, such as photosynthetic and fluorescent proteins, molecular solids, polymers, and bulk liquids. Specifically, we develop universal force fields, QM/MM (quantum mechanics/molecular mechanics), and fragmentation techniques. These methods are broadly applicable to all areas of science and engineering; the resulting computer codes are implemented in the Q-Chem and GAMESS electronic structure packages. We use the developed techniques to investigate fundamental aspects of non-covalent interactions and the effect of the environment on electronic structure. We also employ these tools to solve problems of biological and industrial relevance. We maintain active collaborations with experimental groups, which provide new exciting ideas and inspiration for theoretical developments.