The depletion of natural energy resources, which will eventually lead to a global energy crisis is a serious problem for our society and has driven the search for sustainable and green energy sources. Solar energy is the most favorable alternative to minimize the overexploitation of fossil energy sources. The conversion of solar energy into hydrogen via artificial photosynthesis using a photocatalyst is a promising and sustainable technology to mitigate the global environmental and energy issues. In 1972, titanium dioxide (TiO2) was first explored in electrochemical photolysis for water splitting by Honda and Fujishima and in the following years many other inorganic semiconductors were reported for this purpose. The first organic semiconductor for photocatalytic hydrogen evolution from water was presented in 1985 with poly(pphenylene) but displayed low activity. Later, other metal-free systems like polymeric carbon nitrides, 7 conjugated microporous polymers, and covalent triazine-based frameworks were developed as photocatalysts for HER from water.