Structural steel is a type of steel used to make building materials of various shapes. Many structural steel shapes take the form of long thin beams with a specific cross-section profile. In most industrialized countries, the shape, size, chemical composition, mechanical properties (such as strength), storage methods, etc. of structural steel are regulated by standards.

Most structural steel shapes, such as i-beams, feature a high area of secondary moments; they are very rigid in the installation relative to their cross-sectional area, so they can support high loads without excessive sagging.