The manufacturing of cement demand burning of huge quantities of fuel as well as significant emissions of CO 2 resulting from the decomposition of limestone that consequently resulted in severe environmental impact that is estimated by one ton of CO 2 per ton of cement. Geopolymerization technology is an effective method for converting wastes (containing alumina and silica) into useful products. It can reduce CO 2 emissions significantly from the cement industry. The geopolymerization process usually starts with source materials based on alumina/silicate in addition to alkaline liquids. The compressive strength, setting time, and workability of the final product depends mainly on the type and proportions of the precursors, the type and strength of the activator, the mixing and curing conditions. The structural performance of a geopolymer is similar to that of ordinary Portland cement (OPC). Therefore, geopolymer can replace OPC, and thus decreasing the energy consumption, reducing the cost of the building materials, and minimizing the environmental impacts of the cement industry. This review summaries the mechanism of geopolymerization, including the controlling parameters and different raw materials (fly ash, kaolinite and metakaolin, slag, red mud, silica waste, heavy metals waste, and others) with particular focus on recent studies and challenges in this area. Unlabelled Image • Geopolymer can replace OPC, and thus decreasing energy consumption. • Mechanism of geopolymerization, including the controlling parameters summarized. • Different geopolymer raw materials are thoroughly discussed. • Geopolymer reduces the environmental impact of the cement industry. [ABSTRACT FROM AUTHOR]