In this study, we have performed hybrid functional charged defect calculations on H-doped Li 3 OCl. This is in order to determine the influence of hydrogen on intrinsic defect chemistry of Li 3 OCl and its influence on structure and ionic conductivity. In this model we have considered all vacancies, interstitials, antisites and varying H-related extrinsic species such as singular H, H 2 , OH and HCl. A self-consistent model such as this is highly important for getting a holistic overview of the mechanisms for ionic conductivity as well unravelling the ther- modynamics of Li 3 OCl as given in experimental and computational studies in previous literature. Taking a fully undoped Li 3 OCl we find that across the range of synthesis conditions, (Li-poor to Li-rich), V Li is the dominant charge carrying defect whilst Li i exists in much lower concentrations, thus ruling out an interstitial or interstitialcy mechanism within Li 3 OCl consistent with other reports , despite the lower migration energy barrier of 0.17eV (compared to 0.34eV for V Li ). Under the most Li-rich/anion-poor conditions, the fully Schottky defect exists, [V Li +V O +V Cl ], however with V Cl existing in the neutral charge state. This is somewhat contrary to previous reports of Li 3 OCl being LiCl ([V Li +V Cl ]) Schottky disordered. It is important to note, however, that with the exception of the work in ref. [41], the other studies only consider neutral defects and assume full charge neutrality from V Li and V Cl , yet we find that the positive compensating defect for V Li are oxygen vacancies (V O ). This changes to a Li 2 O Schottky defect([V Li +V O ]) under Li-poor conditions. Equally, whilst antisites are expected to form in small quantities (∼ 10 12 -10 13 cm -3 ) in a fully undoped Li 3 OCl, our results do not point towards significant anion disorder. Concensus in the literature is that anion disorder is beneficial to increasing the conductivity of Li-ion solid electrolytes. This is attributed to significant anion disorder opening up percolating three-dimensional pathways previously inaccessible to anion ordered systems. In a paper by Li et al. they stated that due to the size mismatch between O and Cl, anion antisite defects would cause a strong structural distortion and an electrostatic penalty for mobile lithium defects thus reducing the conductivity.