Knife sharpening is the process of making a knife or similar tool sharp by grinding against a hard, rough surface, typically a stone, or a flexible surface with hard particles, such as sandpaper. Additionally, a leather razor strop, or strop, is often used to straighten and polish an edge. The smaller the angle between the blade and stone, the sharper the knife will be, but the less side force is needed to bend the edge over or chip it off. The angle between the blade and the stone is the edge angle – the angle from the vertical to one of the knife edges, and equals the angle at which the blade is held. The total angle from one side to the other is called the included angle – on a symmetric double-ground edge (a wedge shape), the angle from one edge to the other is thus twice the edge angle. Typical edge angles are about 20° (making the included angle 40° on a double-ground edge). The edge angle for very sharp knives can be as little as 10 degrees (for a 20° included angle). Knives that require a tough edge (such as those that chop) may sharpen at 25° or more.

Different knives are sharpened differently according to grind (edge geometry) and application. For example, surgical scalpels are extremely sharp but fragile, and are generally disposed of, rather than sharpened, after use. Straight razors used for shaving must cut with minimal pressure, and thus must be very sharp with a small angle and often a hollow grind. Typically these are stropped daily or more often. Kitchen knives are less sharp, and generally cut by slicing rather than just pressing, and are steeled daily. At the other extreme, an axe for chopping wood will be less sharp still, and is primarily used to split wood by chopping, not by slicing, and may be reground but will not be sharpened daily. In general, but not always, the harder the material to be cut, the higher (duller) the angle of the edge. It can also be divided into diamond knife sharpener, ceramic knife sharpener and carbide knife sharpener according to the material.

Manual knife sharpeners that are considered to be countertop utensils are also available that are more detailed than the Sharpening Steels. Tools that are built with grinding devices built into plastic or metal cases are often small in size but able to simplify the sharpening activities considerably. Often, the Knife Sharpener will contain a diamond coated abrasive or a tungsten carbide grinding stone for sharpening. A knife is drawn light through the grinding stone at an angle that is preset with the use of guides that keep the knife angle fairly consistent as it is drawn across the sharpening stone. Four to six draws of the blade is usually sufficient to keep the blade well honed. A guard is commonly attached to the sharpener so hands are kept safetly away from the knife blades.

Electric knife sharpeners are another alternative for shapening knifes and are a type of utensil that often simplifies the sharpening process, particularly if the knives are being used frequently for various food cutting activities. Electric sharpeners are designed with basic features for home or moderate use as well as sharpeners built for higher volume usage, such as commercial sharpeners. When selecting consider the size desired, the type of grinding material on the stones, the types of blades that can be sharpened with the device, the safety features, and the ease of cleaning to remove small bits of edge grindings. Lower priced models will contain only one sharpening slot that offer single sharpening features while other models will have sharpening sections for different purposes such as pre-sharpening to remove burrs and old edges before placing the knife in the sharpening or honing section to finish the process. If a knife is to be used only periodically with a minimal amount of cutting, select the lower priced models. However, if the slicing, dicing and cutting chores are frequent, the higher priced or more heavy duty models may be a much better option for keeping all types of knives well sharpened.