The principle for steel beam design is selection of lightest steel beam section that possess sufficient flexural and shear resistance with allowable deflection. Selection of steel beam is simplified by referring to the standard beam sections such as universal I-beams. Their sectional properties are fixed and such tabulation is easily available. Design of steel beam can be complicated if it is not laterally restrained. To design a laterally unrestrained beam, torsional buckling must be considered. By using EuroCode 3, bending resistance of beam section can be modified with factors after the geometry of beam is assessed. This chapter outlines the beam design procedure for both laterally unrestrained and laterally restrained cases. As the first step of design, the boundary condition assessment is focused, which inspects whether the beam is laterally restrained. Then the beam loading calculation is determined based on the fundamental of structural analysis. The evaluation of selected beam section with its flexural and shear resistance, as well as deflection is done with the aids of tables and equations as per EuroCode 3.