The article reviews the precipitation and hardening mechanisms in magnesium alloys, focusing on the structure, morphology, and orientation of precipitates, as well as the effects of these factors on strengthening. It highlights the challenges in understanding the early stages of precipitation and the need for further research to improve the strength of magnesium alloys. The review covers Mg-Al, Mg-Zn, Mg-Zn-Al, and Mg-Ca alloys, detailing the precipitation sequences, microstructural changes, and the impact of alloying elements on the aging response. Despite significant progress, many fundamental issues remain unresolved, particularly regarding the nucleation and growth of precipitates. The article also discusses the rational design of microstructures to enhance the age-hardening response and achieve higher strength.The article reviews the precipitation and hardening mechanisms in magnesium alloys, focusing on the structure, morphology, and orientation of precipitates, as well as the effects of these factors on strengthening. It highlights the challenges in understanding the early stages of precipitation and the need for further research to improve the strength of magnesium alloys. The review covers Mg-Al, Mg-Zn, Mg-Zn-Al, and Mg-Ca alloys, detailing the precipitation sequences, microstructural changes, and the impact of alloying elements on the aging response. Despite significant progress, many fundamental issues remain unresolved, particularly regarding the nucleation and growth of precipitates. The article also discusses the rational design of microstructures to enhance the age-hardening response and achieve higher strength.