There is increased use of blended cements with reduced clinker content in construction as an approach to decrease CO2 emissions associated with cement production. Various supplementary cementitious materials and fillers, with differing physical and chemical properties, can be used in this reduction. A rational scientific approach that considers the properties of materials used is required so as to optimize the combinations, and obtain synergistic effects. The practical use of blended cements should ensure that equivalent, or improved, performance to that of plain Portland cement is obtained. From experimental studies, an increase in workability, lower heat of hydration, high long term strength and improved durability properties have been observed with the use of blended cements. The challenge of attaining these beneficial properties in practice is ensuring proper site practice such as proper curing of structures.