Research on the NIST digital-image-based three-dimensional model of cement hydration and microstructure development (CEMHYD3D) commenced in 1989. CEMHYD3D (Bentz, 1997; Bentz, 2000) is currently recognized as the most extensive, complete, and robust cement paste microstructure model in the world. As such, the model serves as the core of the Virtual Cement and Concrete Testing Laboratory software (Bentz and Forney, 2000). Starting from the measured particle size distribution (PSD) and a detailed scanning electron micrograph (SEM) and X-ray image set for the cement powder, a starting three-dimensional microstructure of cement (which could include other minerals besides portland cement) particles in water is created. The model cement particles match the phase volume fractions, surface fractions, and correlation structures (which give a measure of phase arrangement) measured on the real 2-D cement powder image set. This microstructure is then submitted to the cement hydration model where the user may specify curing conditions in terms of both thermal (semi-adiabatic/adiabatic, isothermal, temperature-defined) and moisture (saturated, sealed) transfer conditions. As hydration executes in the model, a series of output files is created to monitor specific properties as a function of hydration time or achieved degree of hydration. Properties monitored include chemical shrinkage, heat release, setting, capillary porosity percolation, pH and other concentrations of species in pore solutions, and strength development.