Comfortable soft elastic cord. Place the first loop under the chin (Red Arrow) and the second loop over the head (Blue Arrow) with ears draping over the cord. Use the slide adjustment to gently tighten for a firm fit. The white center wedge in the center of the glasses (Hint: It will have a paw imprint ) should slide effortlessly into the crease found between your dogs two eyes. This will keep the lenses centered during movement and maximize stability and comfort for your dog.