The seismic behaviour of moment-resisting and eccentrically-braced steel frames is studied. Inelastic time history analyses are presented to show that simple design techniques may be developed to encourage earthquake resisting structures to behave well, even though their seismic response may be complex. Complementary to the analytical study, eight steel I-section beam-columns were tested under a regime of cyclic bending. The units exhibited very good hysteretic behaviour prior to their failure by means of fracture or various modes of buckling. The cyclic post-elastic behaviour of beams and beam-columns in steel multistorey frames, and some parameters influencing their deformation capacity are discussed.