Installing wallpaper on a staircase can be a bit challenging, but it is possible with some careful planning and attention to detail. Start by measuring the height and width of each stair riser and tread, and cut the wallpaper to fit each individual stair. Apply the wallpaper paste to the surface and carefully smooth the wallpaper into place, using a wallpaper smoothing brush or seam roller to remove any air bubbles or wrinkles. Repeat the process for each individual stair, taking care to ensure that the pattern lines up perfectly with the previous stair.