We focus on the development and application of new electronic structure theories. Specifically, we are interested in multi-scale models, which allow for the study of large and extended systems. We are developing quantum-embedding theories, which treat different regions of the system at different levels of accuracy. This allows for a high chemical accuracy in a small region, such as an active site of a catalyst, and a less accurate, but more computationally efficient description of the remainder. These tools can then be used to perform first-principle studies on large, reactive, and condensed phase systems. We are interested in applying these methods to metalloenzymes, heterogeneous catalysts, and metal-organic frameworks.