Polymeric　graphitic　carbon　nitride　(for　simplicity,　g-C　3N　4)　is　a　layered　material　similar　to　graphene,　being　composed　of　only　C,　N,　and　some　impurity　H.　Contrary　to　graphenes,　g-C　3N　4　is　a　medium　band　gap　semiconductor　and　an　effective　photocatalyst　for　a　broad　variety　of　reactions,　and　it　possesses　a　high　thermal　and　chemical　stability　In　this　Perspective,　we　describe　the　polycondensation　of　this　structure,　how　to　modify　band　positions　and　band　gap　by　doping　and　copolymerization,　and　how　to　texture　the　organic　solid　to　make　it　an　effective　photocatalyst.　We　then　describe　the　photochemical　splitting　of　water　and　some　mild　and　selective　photooxidation　reactions　catalyzed　by　g-C　3N　4.　©　2012　American　Chemical　Society.