In　the　past　decade,　research　in　the　field　of　artificial　photosynthesis　has　shifted　from　simple,　inorganic　semiconductors　to　more　abundant,　polymeric　materials.　For　example,　polymeric　carbon　nitrides　have　emerged　as　promising　materials　for　metal-free　semiconductors　and　metal-free　photocatalysts.　Polymeric　carbon　nitride　(melon)　and　related　carbon　nitride　materials　are　desirable　alternatives　to　industrially　used　catalysts　because　they　are　easily　synthesized　from　abundant　and　inexpensive　starting　materials.　Furthermore,　these　materials　are　chemically　benign　because　they　do　not　contain　heavy　metal　ions,　thereby　facilitating　handling　and　disposal.　In　this　Review,　we　discuss　the　building　blocks　of　carbon　nitride　materials　and　examine　how　strategies　in　synthesis,　templating　and　post-processing　translate　from　the　molecular　level　to　macroscopic　properties,　such　as　optical　and　electronic　bandgap.　Applications　of　carbon　nitride　materials　in　bulk　heterojunctions,　laser-patterned　memory　devices　and　energy　storage　devices　indicate　that　photocatalytic　overall　water　splitting　on　an　industrial　scale　may　be　realized　in　the　near　future　and　reveal　a　new　avenue　of　post-silicon　electronics＇.　©　017　Macmillan　Publishers　Limited,　part　of　Springer　Nature.　All　rights　reserved.