Data from published literature and laboratory tests regarding use of limestone in portland cement are reviewed. Emphasis is placed on amounts of 5% or less. The effects of interground and blended limestone on the particle size distribution of cement and workability of mortar and concrete are reported. Hydration behavior is examined with regard to chemistry, heat evolution, microstructure, and setting time. The properties of hardened mortar and concrete made with limestone portland cement are examined and compared to those made with non-limestone portland cements–including compressive and flexural strength, volume stability, durability (permeability, carbonation, freeze/thaw resistance, sulfate and chloride resistance, and alkali-silica reaction), and interactions with mineral and chemical admixtures. Quality control of the limestone, limestone portland cement, and concrete is also discussed. In general, the use of up to 5% limestone does not affect the performance of portland cement. Strengths of cements with limestone can be optimized by grinding to an appropriate particle size distribution. An optimized portland cement containing up to 5% limestone can exhibit improvements in workability as compared to the same cement without limestone. Energy requirements for both pyroprocessing and comminution are reduced by the use of limestone.