The reaction OH- + CH2F2 --> products has been investigated by both selected ion flow tube (SIFT) experiments and ab initio molecular calculations. The SIFT experiments showed that a bimolecular process, leading to two major anionic products, CHF2- (86%) and F- (11%), and one minor anionic product, HF2-(3%), is in competition with a three-body association leading to OH-. CH2F2 (where values in parentheses are the relative values of the detected anionic products at 300 K). From a pressure dependence study, an upper limit of the bimolecular reaction rate coefficient at 300 K is determined to be (2.4 +/-1.4) x 10(-12) cm(3) molecule(-1) s(-1). This shows a small negative temperature dependence, suggesting that the reaction proceeds via an ion-complex intermediate. These experimental results were rationalized using ab initio molecular orbital calculations. Stationary points on the reaction paths of the two main reaction channels were located at both the HF/6-31++G** and MP2/6-31++G** levels. The relative energies of the located stationary points were calculated at up to the CCSD(T)/6-311++G(3df,2p)//MP2/6-31++G** level. The CHF2- + H2O channel was found to be endothermic by 7.5 kcal mol(-1) and the F- + CH2(OH)F channel was found to be exothermic by 20.4 kcal mol(-1). It was found that both reaction channels proceed via the reactant-like ion-molecule complex intermediate, OH-. CH2F2, in agreement with the conclusion drawn from the experimental negative temperature dependence of the overall rate coefficient. The fact that the product anion yields show that [CHF2-] > [F-], despite the fact that the CHF2- + H2O channel is endothermic whereas the F- + CH2(OH)F channel is exothermic, has been rationalized using transition-state theory.