Security barrier apparatus (10) comprising a support (12, 14) and a barrier member (18, 20) movable relative to the support between a stowed position and a deployed position, the support (12, 14) having an upper part (16) for positioning substantially at ground level. The barrier member (18, 20) has at least two telescopic posts one within the other, the inner post (20) being lowermost in the deployed position. A linkage is provided between an outer post (18) and the inner post (20). In use, motion of the outer post (18) between the stowed position and the deployed position causes corresponding motion of the inner post (20).