In this review we describe CO on NaCl(100) as a model system for the exploration of surface structure and vibrational energy flow patterns. The system has been studied by a wide variety of surface science techniques in recent years. Thermodynamic measurements reveal the surface bond strength and polarized infrared spectroscopy demonstrates that the CO axis is perpendicular to the (100) face. Infrared photometry provides the radiative rate of the vibrationally excited CO monolayer on NaCl(100). Temperature-dependent bandshape measurements contain information on the dephasing rate. Several experiments in which the monolayer is vibrationally excited by a laser yield the phonon relaxation rate and provide an upper limit on the photodesorption rate. Infrared fluorescence from the excited monolayer has been monitored. The bond strength measurements, structure determinations, infrared band profile studies and the mapping ofallthe vibrational relaxation channels of CO on NaCl(100) comprise an unusually complete catalogue of experimental results. These results are used to test theoretical models that calculate structure and bonding, spectroscopic bandshapes and relaxation rates—with mixed success. CO on NaCl(100) appears unique among surface systems in that it is accessible to a wide variety of experimental explorations. Some of the theoretical models seem quantitatively reasonable but others, which may be qualitatively correct, need further development.