Slender plate girders are frequent elements of steel structures. Welded slender plate girders without transverse and longitudinal stiffeners have technological advantages. The aims of book are analytical-experimental investigation of welded slender plate girders subjected to uniformly distributed edge loading without transverse stiffeners and the development of the calculation requirements. The post-buckling behaviour of slender plate girders is considered. Research concentrated on examining the behaviour of slender plate girders in conditions, which are close to the real situation. The idea is to consider real loading and boundary conditions concerning girders web which stress field is strictly influenced by compression, flexural and torsional rigidity of girder’s flange and compare numerical results of the continuous analytical and the finite element method with results obtained from Eurocode 3 formulas and with the test results.