Magnesium and magnesium alloys have been employed in a wide variety of structural applications because of their favorable combination of tensile strength, elastic modulus, and low density. Providing a brief section on occurrence, production, and uses of magnesium, this article describes alloy and temper designations of cast and wrought magnesium alloys. The role of mechanical properties and fabrication characteristics in selection of product forms for structural applications is covered. The article explores the use of magnesium alloys as a substitution for heavier metals such as steel and aluminum alloys to reduce weight in structural parts.