<p>Selective laser melting (SLM) of magnesium (Mg) and its alloys presents a transformative approach for fabricating lightweight, biocompatible components, yet is fundamentally challenged by magnesium's inherent volatility and high reactivity. This review critically assesses the state-of-the-art, establishing the scope of SLM for Mg alloys by examining the intricate links between processing parameters, resultant microstructures, and final properties. Key findings reveal that the narrow and sensitive processing window is a primary source of defects, including porosity, elemental loss, and cracking, which compromise material integrity. The rapid solidification characteristic of SLM yields fine-grained, non-equilibrium microstructures, offering enhanced strength over conventionally processed counterparts. However, this is frequently offset by poor as-built ductility due to processing defects. Furthermore, the corrosion and biodegradation behaviour is exceptionally complex; the unique microstructures and defects can induce unpredictable, accelerated degradation, which is a significant hurdle for biomedical applications where controlled performance is critical. The significance of this review lies in its synthesis of these process-structure–property relationships. It highlights that achieving reliable performance for demanding aerospace and biomedical applications depends critically on mitigating defects through advanced process control, innovative alloy design, and optimised post-processing strategies to unlock the full potential of this advanced manufacturing technology.</p>