Ab initio calculations are used to examine the energetics of unimolecular and water-mediated decomposition of CF3OH into COF2 and HF. The calculations indicate that the barrier to unimolecular decomposition is large (42 +/- 3 kcal mol(-1)) and that the rate of this reaction is negligible at room temperature. This reaction is of no importance under ambient atmospheric conditions. The calculations also reveal a substantially lower energy pathway for decomposition that is accessible via a reaction between CF3OH and water. This pathway involves formation of a six-membered-ring transition state, with water acting as a bridge between the fluorine and hydrogen of the alcohol. The existence of this lower energy pathway is consistent with experimental evidence for the intermediacy of H2O in the decomposition of CF3OH. From the computational results the second-order rate constant for homogeneous decomposition can be estimated to lie in the range 10(-27) to 10(-22) cm(3) molecule(-1) s(-1) at 298 K and is likely too small to be atmospherically significant. The rate for heterogeneous decomposition cannot be estimated from the computational results, but the results are consistent with a prominent role for heterogeneous decomposition in the atmospheric chemistry of CF3OH.