Low-carbon cementitious materials are a family of cementitious binders and constituents formulated or selected to reduce greenhouse-gas emissions expressed as CO₂-equivalent associated with cement and concrete production, relative to a specified conventional baseline, while providing the binding performance required for their intended applications ^[1]. Emission reductions can be achieved primarily by lowering the Portland-clinker fraction through partial replacement with supplementary cementitious materials, such as fly ash, ground granulated blast-furnace slag, silica fume, metakaolin, and calcined clay, or by using alternative binder chemistries, including alkali-activated binders, calcium sulfoaluminate cements, belite-rich cements, and magnesium-based cements, which may require lower calcination temperatures or reduce reliance on limestone calcination ^[2]. Because conventional Portland cement production generates greenhouse-gas emissions from both the calcination of calcium carbonate and fuel combustion during clinker production, the low-carbon performance of a cementitious material is generally assessed by comparing greenhouse-gas emissions with those of an appropriate baseline, using a defined system boundary and functional unit ^[3][4][5]. Such comparisons should also consider equivalent performance requirements, including strength, durability, and expected service life, to ensure that emission reductions are evaluated on a functionally comparable basis. Low-carbon cementitious materials therefore do not correspond to a single composition, clinker-substitution level, or strength class, and conventional blended cements may also be considered low-carbon when they demonstrate a meaningful reduction in greenhouse-gas emissions relative to an appropriate reference system.