Abstract: A stair-climbing and descending vehicle is disclosed, comprising a frame and a pair of transverse, co-axial, power-driven axles, each rotatably carrying a spider assembly at its outer end. Each spider has at least three wheels, one at each equi-spaced extremity of its radial arms. Each axle drives either the spider or the associated wheels through a differential gearing. When climbing a stairway, the spiders are rotated immediately when the wheels are prevented from rotating by encountering a stair riser. The differential also serves to safety and smoothly descend the stairs. The vehicle is adapted for use as a wheelchair, in which case a chair-shifting device is provided to shift the center of gravity of the vehicle, rearwardly.