The interaction of methanethiol, CH3SH, with Cu(100) has been studied by S 1s photoemission, S K-edge near-edge x-ray absorption fine structure and normal-incidence standing x-ray wavefield absorption at both (200) and (111) reflections. The results indicate that a single methanethiolate species, CH3S-, is formed and this is bonded to the unreconstructed surface via the S atoms which adopt the fourfold symmetric hollow site. This conclusion confirms the results of a recent near-edge and surface extended x-ray absorption fine structure study, but contrasts with the established adsorbate-induced reconstruction produced by this species on Cu(111).