The thermal, electron, and photon-induced chemistry of cyclopropane, c-C3H6, adsorbed on Pt(111) at 100 K has been studied. The thermal chemistry is simple. Adsorption is saturable, no multilayer accumulates, and thermal desorption exhibits only c-C3H6 with one peak at 144 K. High-resolution electron energy loss spectra results indicate that c-C3H6 adsorbs with the plane of the ring tilted away from the surface normal. The electron-induced chemistry is more complex. Irradiation with 50 eV electrons activates dissociation of adsorbed c-C3H6 at 100 K, and there are thermally activated reactions during subsequent temperature-programmed desorption. The total cross-section for destruction of c-C3H6 is 8.2 (+/-0.2) x 10(-17) cm(2). For low electron fluences, <10(16) cm(-2), the chemistry involved is describable in terms of C-C bond breaking to open the ring and form metallacyclic species, some of which promptly lose H to form allylic (C3H5) moieties. In subsequent thermally activated reaction-limited processes, propylene, methane, ethylene, and hydrogen desorb. Only carbon remains above 800 K. Activation with 6.4 eV (193 nm) photons is also effective, but the cross section for loss of C-C3H6 is nearly 4 orders of magnitude lower than that for electron irradiation.