This collection from the 12th International Conference on Magnesium Alloys and Their Applications (Mg 2021)—the longest running conference dedicated to the development of magnesium alloys—covers the breadth of magnesium research and development, from primary production to applications to end-of-life management. Authors from academia, government, and industry discuss new developments in magnesium alloys and share valuable insights. Topics in this volume include but are not limited to the following: Primary production Alloy development Solidification and casting processes Forming and thermo-mechanical processing Other manufacturing process development (including joining and additive manufacturing) Corrosion and protection Modeling and simulation Structural, functional, biomedical, and energy applications Advanced characterization and fundamental theories Recycling and environmental issues