Infrared-visible sum-frequency spectroscopy (SFS) has been used to obtain vibrational spectra in the C-H stretching region of surfactants adsorbed at the solid-water interface All of the surfactants formed monolayers at a hydrophobic substrate with the hydrocarbon chains of the surfactant oriented away from the aqueous phase. Surfactants with a wide range of structures have been examined, including cationic, anionic, nonionic, and zwitterionic head groups and single, double, and branched alkyl chains. Features in the C-H stretching region originate principally from the hydrocarbon chains and not from the polar head groups. The packing density and the orientational order of the surfactant monolayers is deduced from the relative strengths of the chain methylene and terminal methyl modes. The structure of the monolayers adsorbed at a flat, hydrophobic surface is compared to surfactant aggregates in bulk aqueous solution, at the air-water interface and in the solid crystalline state.