Abstract: A ski is disclosed for efficiently sailing on snow or ice. The ski has greater thickness than a conventional downhill ski. The substantially triangular shape of the cross-section of the ski is longitudinally constant so as to generate simultaneously both lift and lateral forces with minimum drag. The surface of the ski in contact with the snow or ice is made from or treated with a low friction material. The ski has a longitudinally upward concave curvature to facilitate turning. The ski tip is formed with deadrise like the bow of a boat or, in the alternative, may be a thin shovel like the tip of a conventional ski. The ski incorporates an edge or blade extending downwardly below the central part of the ski to enhance the lateral to drag force ratio on ice.