▪ Abstract  The entrance channel to the OH + H2 → H2O + H hydrogen abstraction reaction has been investigated from several different experimental approaches and complementary theoretical calculations. Weakly bound complexes between the hydroxyl radical and molecular hydrogen have been stabilized within a shallow well in the entrance channel and characterized via electronic spectroscopy on the OH A²Σ⁺ − X²Π transition. Laser-induced fluorescence and fluorescence depletion experiments have revealed the binding energy of H2/D2 with ground state OH X²Π radicals, the intermolecular energy levels supported by the OH A²Σ⁺ (v′ = 0,1) + H2/D2 potential, and the OH-H2/D2 excited state dissociation limit. The OH X²Π + H2 potentials have also been examined through inelastic scattering measurements on Λ-doublet state–selected OH with normal or para-H2. Finally, photodetachment of an electron from the H3O⁻ anion enabled the neutral reaction to be probed in conformations sampled by the two isomeric forms of the anion.