This book describes different strategies for the reductive part of the artificial photosynthesis. The first system is the intramolecular approach. In an intramolecular approach the two relevant active centres are connected with each other in one molecule. The two active centres are the photosensitiser and the water reduction catalyst. The photosensitiser interacts with the sunlight and transfers the energy and the electron to the water reduction catalyst, which reduces the protons from the water to elementary hydrogen. The second system is the intermolecular approach. There, the two active centres (photosensitizer, water reduction catalyst) are separated in two different molecules and are only able to react after a collision. All the systems were analysed and a catalytical pathway as well as the energy and electron transfer could be analysed. Another very important goal of this work was the exchange of noble metals like Osmium, Palladium and Iridium with earth abundant metals like Iron, Cobalt and Copper.