Numerous researchers around the globe are focusing their efforts toward the development of renewable energy sources. Among them are devices that harvest sun light and use it to split water into molecular hydrogen and oxygen. Thereby water oxidation is believed to be one of the bottlenecks that needs to be overcome through the development of appropriate catalysts. An in-depth understanding of the fundamental properties of those catalysts is crucial in order to improve them further or to design novel catalysts with high catalytic activity and stability. Theoretical studies offer a great opportunity, to elucidate the structure and dynamics of the catalyst, the catalytic mechanism, and the properties of potential intermediates. In this chapter, we describe our recent efforts for advanced modeling of catalysis and how the combined effort of experimental and computational work can lead to a better understanding of the catalysts at hand and development of new catalysts. Thereby we focus on two families of catalysts studied by our group. First we introduce tetranuclear Co(II)-based water oxidation catalysts featuring a cubane core as found in the oxygen evolving complex of nature's photosystem II. Afterward, we discuss selected mononuclear Ru(II)-based water oxidation catalysts.