The interaction of ethylene with the (100), (110), (111), and (211) faces of tungsten was studied by means of thermal desorption spectroscopy. Ethylene decomposition yields a single broad hydrogen peak at ∼300 K on W(111), two poorly resolved hydrogen peaks at ∼300 and ∼400 K on W(211), hydrogen peaks at ∼300 and ∼450 K with an area ratio of 1:2 on W(110), and a single decomposition peak at ∼275 K on W(100). Assuming di-σ-bonded ethylene, these results are consistently interpreted in terms of the limitations on ethylene adsorption imposed by the structure of the surface; and the stability of adsorbed ethylene is interpreted from consideration of the structure of the resulting ethylene-surface complex. The absence of two equal peaks on all except the (211) face eliminates the possibility of a two-step decomposition suggested by previous work.