Gas-phase reactivity of the copper hydride anions [CuH] and [CuH] toward a range of neutral reagents has been examined via multistage mass spectrometry experiments in a linear ion trap mass spectrometer in conjunction with isotope labeling studies and Density Functional Theory (DFT) calculations. [CuH] is more reactive than [CuH], consistent with DFT calculations, which show it has a higher energy HOMO. Experimentally, [CuH] was found to react with CS via hydride transfer to give thioformate (HCS) in competition with the formation of the organometallic [CuCS] ion via liberation of hydrogen; CO via insertion to produce [HCuOCH]; methyl iodide and allyl iodide to give I and [CuHI]; and 2,2,2-trifluoroethanol and 1-butanethiol via protonation to give hydrogen and the product anions [CuH(OCHCF)] and [CuH(SBu)]. In contrast, the weaker acid methanol was found to be unreactive. DFT calculations reveal that the differences in reactivity between CS and CO are due to the lower lying π* orbital of the former, which allows it to accept electron density from the Cu center to form the initial three-membered ring complex intermediate, [HCu(η-CS)]. In contrast, CO undergoes the barrierless side-on hydride transfer promoted by the high electronegativity of the oxygen atoms. Side-on S2 mechanisms for reactions of [CuH] with methyl iodide and allyl iodide are favored on the basis of DFT calculations. Finally, the DFT calculated barriers for protonation of [CuH] by methanol, 2,2,2-trifluoroethanol, and 1-butanethiol correlate with their gas-phase acidities, suggesting that reactivity is mainly controlled by the acidity of the substrate.