The adsorption and decomposition of methylsilane gas onto Cu(111) has been investigated by reflection-absorption infrared spectroscopy (RAIRS). The initial adsorption of methylsilane at 15 K results in the formation of an initially ordered physisorbed monolayer, adsorbed with a small tilt angle from the plane of the surface. Further increase in exposure results in the formation of a more dense monolayer, with methylsilane lying nearly parallel to the surface of the crystal, before the growth of the disordered multilayer. Adsorption at 78 K appears to result in the formation of an SiH-CH3 species for which there is some evidence of further Si-Si coupling. At 295 K, methylsilane is observed to adsorb with the Si-C axis perpendicular to the surface. Adsorption at 395 K results in the decomposition of methylsilane, with both Si-H and Si-C bond scission. Adsorbing CO at 15 K on the Cu/Si surface structure thus formed indicates that CO adsorbs mostly in atop positions on Si atoms, suggesting that any metal atom sites are blocked by either adsorbed C or Si atoms.