Raman spectra of single-phase calcium-silicate hydrate (C-S-H) samples with C/S ratios between 0.88 and 1.45 are consistent with a defect tobermorite model for the structure of these materials, in agreement with previously published nuclear magnetic resonance (NMR) spectroscopic data for the same samples. The Raman spectra of C-S-H samples with C/S ratios <1.0 are very similar to those of 14z~ tobermorite. Those of C-S-H samples with C/S ratios 91.0 show substantial concentrations of both Q1 and Q2 Si sites and indicate the possible presence of jennite-like environments. Raman spectroscopy, like infrared and NMR, is a probe of local structure on the atomic nearest neighbor and next-nearest neighbor scale, and thus provides significantly different information than diffraction methods. The Raman spectra of the C-S-H have a rich structure and contain peaks for Si-O stretching, Si-O-Si bending, internal deformation of the Si-O tetrahedra and Ca-O polyhedra, and characteristic peaks at lower frequencies. The spectra of jennite and 144 tobermorite are quite similar, confirming the result from NMR spectroscopy that jennite has dominantly Q2 polymerization. The Raman spectra qf 114 and 14A tobermorite are also similar, although our sample of 114 tobermorite has a significant concentration of Q3 Si sites, which indicates cross-linking of the chains. ADVANCED CEMENT BASED MATERIALS, 1997, 5, 93-99.