This chapter explores the properties, development, and automotive applications of magnesium and its alloys. Magnesium offers superior castability, high specific strength, and exceptional vibration damping as the lightest structural metal. Alloying elements such as aluminum, zinc, manganese, and rare earths enhance its mechanical properties and corrosion resistance. Historical applications in the automotive and aerospace industries have evolved. Magnesium components are now featured in engine blocks, transmission cases, wheels, seat frames, and structural body parts, significantly reducing vehicle weight. Despite challenges like flammability and creep resistance, continuous alloy development and advanced manufacturing have driven magnesium’s resurgence. Detailed industrial examples illustrate its integration in body, chassis, powertrain, and interior systems. The chapter underscores magnesium’s critical role in lightweight, fuel-efficient vehicle design and the ongoing evolution of high-performance magnesium alloys.