Taking the Hall-Petch relationship as a starting point, the factors contributing towards Mg alloy strengthening are analysed, and their relative importance quantified. Solid-solution strengthening is modelled employing a power-law approach. The effects of various processing schedules are reviewed, showing that these play a relatively minor role. Grain refinement effects are described employing thermodynamic and kinetic formulations via the interdependence theory approach. The effects of rare earths are examined, showing that their major contribution is towards grain size control, an effect often in conflict with solid-solution strengthening. A computational approach is proposed, successfully modelling 104 grades reported in the literature. The approach may aid in tailoring and designing Mg alloys for yield strength.