Here, we present a combined theoretical and experimental investigation of the intrinsic and extrinsic point defect chemistry of t-Se. We start by characterising the bulk electronic structure and allotropic phase behaviour, finding anisotropy and deformability to be key factors connected to PV performance. This is followed by an analysis of the intrinsic point defect thermodynamics, along with their impact on non-radiative electron-hole recombination, revealing the benign nature of intrinsic point defects. Lastly, we investigate the behaviour of impurity species in t-Se, through experimental measurements of elemental distributions in high-quality selenium films, and first-principles predictions of solubility and doping behaviour. We find that point defects, whether intrinsic or extrinsic, cannot explain the reported carrier concentrations in Se films. Interpreting our results in the context of recent experiments, we propose that extended defects and interfaces are the current limiting factors for efficiencies in t-Se devices.