The graphitic carbon nitride (g-C₃N₄) which is a two-dimensional conjugated polymer has drawn broad interdisciplinary attention as a low-cost, metal-free, and visible-light-responsive photocatalyst in the area of environmental remediation. The g-C₃N₄-based materials have excellent electronic band structures, electron-rich properties, basic surface functionalities, high physicochemical stabilities and are “earth-abundant.” This review summarizes the latest progress related to the design and construction of g-C₃N₄-based materials and their applications including catalysis, sensing, imaging, and white-light-emitting diodes. An outlook on possible further developments in g-C₃N₄-based research for emerging properties and applications is also included.