Ab initio calculations of portions of the C2H5O potential energy surface critical to the title reaction are presented. These calculations are based on QCISD geometries and frequencies and RQCISD( T) energies extrapolated to the complete-basis-set limit. Rate coefficients for the reaction of C2H4 with OH are calculated using this surface and the two transition-state model of Greenwald and co-workers [J. Phys. Chem. A 2005, 109, 6031] for the association of OH with C2H4. The present calculations reproduce most of the experimental data, including the temperature and pressure dependence of the rate coefficients, with only a small (0.4 kcal/ mol) adjustment to the energy barrier for direct hydrogen abstraction. We confirm the importance of this channel above 800 K and find that a significant fraction of the total rate coefficient (similar to 10%) is due to the formation of vinyl alcohol above this temperature. Calculations of the vinyl alcohol channel are consistent with the recent observation of this molecule in low-pressure flames [Taatjes, C. A.; Hansen, N.; McIlroy, A.; Miller, J. A.; Senosiain, J. P.; Klippenstein, S. J.; Qi, F.; Sheng, L.; Zhang, Y.; Cool, T. A.; Wang, J.; Westmoreland, P. R.; Law, M. E.; Kasper, T.; Kohse-Hoinghaus, K. Science 2005, 308, 1887] and suggest that this reaction should be included in hydrocarbon oxidation mechanisms.