This chapter describes steel's properties, classifications, and applications in the automotive industry, emphasizing its central role due to its strength, cost-effectiveness, and adaptability. It outlines the evolution from conventional steels to advanced high-strength steels, including dual-phase, transformation-induced plasticity, complex phase, martensitic, and twinning-induced plasticity steels. Special attention is given to structural performance, formability, and crash resistance. The chapter also details specific chemical compositions, microstructures, and mechanical properties of progressive steel types and highlights ongoing innovations. Steel remains the dominant material for automotive structures due to continuous advancements in its performance and manufacturing capabilities.