The behavior and design of hot-rolled and cold-formed steel square and rectangular hollow section (SHS and RHS) columns,made ofbothnormal and high strength material,are addressed in this paper. A series ofexperimentson hot-rolled high strength steel SHScolumns was first conducted–six tests on S690 SHS 100×100×4 columns and six tests on S770 SHS 120×120×6.3columns were performed. Finite element (FE) models were developed to replicate the experimental results and to carry out parametric studies to expand the column buckling data pool. The accuracy of the European and North American buckling design rules for normal and high strength steel SHS and RHS columns wasevaluated through comparisons with the freshly generated test and FE results,as well as with existing testdatacollected from a literature.Finally, amodified Eurocode 3(EC3)approach wasproposedand statistically verified in accordance with EN 1990; the new approach features an imperfectionfactor that is a continuous function of yield strength, reflecting the reducing relative influence of residual stresses and global imperfections with increasing steel grades. Improvedconsistency in resistance predictions over the existing design provisions is demonstrated acrossa widerange of steel gradesand relative slenderness values.