From now on, the case study of overall water splitting (OWS) is considered. The sunlightdriven overall splitting of water in H 2 and O 2 is often referred to as the "Holy Grail" in the energy landscape, as it is a renewable way of generating energy carriers in a simple but robust strategy from clean and widely available energy sources. Although OWS for COFs does not come without challenges, e.g., slow kinetics of OER and insufficient driving force from photogenerated charge carriers, this case study can guide the discussion, especially for the preliminary evaluation of thermodynamic feasibility. This can be evaluated by band edge alignment with the redox potentials of the reaction. An analogous analysis could be applied to any pair of redox reactions, also with sacrificial agents, co-catalysts, and in a Z-scheme.