Magnesium has proved to be a good candidate as an orthopaedic implant due to its tensile strength, weight-bearing ability, cytocompatibility, and biodegradability. However, magnesium degrades too rapidly in vivo to match bone growth rate, which can lead to pain, inflammation, and implant failure. Calcium phosphate-based coatings offer a possible mechanism to reduce the degradation of magnesium implants in vivo while promoting bone growth. Octacalcium phosphate is a precursor to hydroxyapatite, the calcium phosphate phase that forms the mineral component of bone. This project aims to design and characterise an octacalcium phosphate coating and apply it to magnesium alloy WE43 specimens using an immersion method, then investigate the degradation of the coated implants in simulated physiological conditions. Octacalcium phosphate was synthesised using the dropwise addition of calcium acetate monohydrate to a sodium dihydrogen phosphate anhydrous solution. An immersion process for coating metallic implants was developed by submerging the implant in the stirred octacalcium phosphate reaction solution for the duration of the reaction. A design of experiment approach was then used to investigate the optimal parameters of the coating process. The resulting optimised coated magnesium specimens underwent a degradation study in Hank’s balanced salt solution at 37°C. The degradation of the implants was quantified by measuring the mass loss of magnesium throughout the degradation. SEM and XRD spectroscopy were used to investigate the formation of an apatite on the implant's surface. The coating method produced a pure octacalcium phosphate coating on the WE43 samples with a calcium/phosphate ratio of 1.33, and good adhesion and a thickness of 1.802 μm. The degradation study showed that the octacalcium phosphate coating significantly reduced the degradation of magnesium, and the octacalcium phosphate coating fully transformed into hydroxyapatite after seven days of immersion in Hank’s balanced salt solution.