The reaction of atomic hydrogen with acetonitrile has been studied using the B3LYP and Gaussian-3 (C3) methods. The geometries and vibrational frequencies of various stationary points on the potential energy surface were calculated at the B3LYP level with the 6-311G(d,p) and 6-311++G(2d,2p) basis sets. The energetics were refined at the G3 level. The G3 barrier height has been calibrated using a test set including 39 well-established reactions. It is believed that the present potential energy surface is reliable within chemical accuracy. The title reaction starts in four manners, namely direct hydrogen abstraction, C-addition, N-addition, and substitution. The corresponding barrier heights (including ZPE corrections) are 12.0, 7.6, 9.6, and 44.7 kcal/mol, respectively. The kinetics of the reaction were studied using the TST and multichannel RRKM methodologies over the temperature range 300 similar to 3000 K, and were compared with the earlier experimental data. At lower temperatures, the C-addition step is the most feasible channel, and the major products are CH3 and HCN at lower pressures. At higher temperatures, the direct hydrogen abstraction path leading to H-2 and CH2CN is apparently dominant.