Abstract: A sole attachment or undersupport in the form of a plate attached to the sole of footwear, in particular a ski boot, wherein the lower tread or walking surface is domed in the direction of the sole. The plate is provided with holder elements which engage over the sole. One of the holder elements is rigid, the other holder element is movable. Fixing means, for instance pins are provided, which engage into bores provided at the ski boot sole. The plate consists of telescopically adjustable plate portions. There are also provided recesses in the tread surface and adjustable anti-skid elements, such as adjustable pins serving to prevent slipping or skidding by the user. Holders can be provided for securing the sole attachment at a ski when it is not worn at the ski boot or the like.