Abstract: An adjustable lumbar support for the backrest of a seat, including an elongate flexible band having first and second ends attachable to sides of a backrest. A drive member is connected to the band so as to tension the band and so decrease the extent to which the band curves rearwardly with respect to the ends thereof. The band includes a plurality of pleats, extending transverse to the length of the band and arranged to expand or collapse in response to changes in the longitudinal tension in the band. As shown, the pleats form part of a shield overlying a tensionable strap. In another arrangement (not shown) the pleats are disposed between and interconnect adjacent relatively rigid rib-like elements. The drive may include a motor driving a screw-threaded spindle arranged at right angles thereto and connected to the band so that the spindle extends in the longitudinal direction of the band. A carriage responds to rotation of the spindle so as to tension the band.