Magnesium-based metals, including pure magnesium and its alloys, are becoming increasingly popular in the medical industry due to the fact that they are biodegradable. This chapter briefly introduces the concept of biodegradable magnesium-based metals and their advantages as a new class of metallic biomaterials. Relevant research progress is summarized, especially the corrosion control of magnesium-based metals by appropriate surface modification, which is a key issue for clinical applications.