The containment of chromium in tricalcium silicate (C 3 S 1 ) has been investigated. Tricalcium silicate is a major component in ordinary Portland cement (OPC), and chromium compounds used as dopants simulate chromium wastes that might be stabilized in a cement matrix. Scanning electron microscopy (SEM) and energy dispersive X-ray spectroscopy (EDS) were used to probe the distribution of chromium in the stabilized waste form and also to identify the microstructural changes in the normal hydration products of C 3 S accompanying the addition of chromium as Cr(III) and Cr(VI). X-ray diffraction (XRD) was used to monitor the hydration reaction of C 3 S and formation of crystalline calcium hydroxide (CH). The effect of chromium addition on the condensation of the orthosilicate units in C 3 S was followed with Fourier transform infrared spectroscopy (FTIR). Standard acetic acid leaching tests were carried out to evaluate the mobility of chromium in the Cr(III) 3 S and Cr(VI) 3 S systems. Probable mechanisms of chromium containment in the amorphous calcium silicate hydrate (C-S-H) phase are discussed.