Abstract: A knife sharpener having a clamp system held by a frame in such a way that the knife to be sharpened may move in any direction freely but is otherwise held so that it does not rotate about any axis through the knife in order to maintain its orientation with respect to sharpening stones held by the frame. The knife can therefore be sharpened by moving it toward the user and down, first against one of two stones and then against the other, opposing stone, to sharpen both sides of the blade. The sharpener can be attached to a base or to the underside of cabinetry and may be used with various sharpening stones. In particular, a triangular, pivoting stone with rounded corners is preferred because it offers different facets and curves for use in sharpening flat-bladed and serrated knives and fully engages the knife blade through to the tip as the blade is drawn across its surface.