Sharpening stones, or whetstones, are used to sharpen the edges of steel tools such as knives through grinding and honing.

Such stones come in a wide range of shapes, sizes, and material compositions. They may be flat, for working flat edges, or shaped for more complex edges, such as those associated with some wood carving or woodturning tools. They may be composed of natural quarried material or from man-made material. They come in various grades, which refer to the grit size of the abrasive particles in the stone. (Grit size is given as a number, which indicates the spatial density of the particles; a higher number denotes a higher density and therefore smaller particles, which give a finer finish to the surface of the sharpened object.) Stones intended for use on a workbench are called bench stones, while small, portable ones, whose size makes it hard to draw large blades uniformly over them, especially “in the field,” are called pocket stones.

Often whetstones are used with a cutting fluid to enhance sharpening and carry away swarf. Those used with water for this purpose are often called water stones or waterstones, those used with oil sometimes oil stones or oilstones.

Whetstones will wear away with use, typically in the middle. Tools sharpened in this groove will develop undesirable curves on the blade. In order to prevent this, a whetstone may be levelled out with sandpaper or a levelling or flattening stone.