Steel wool or 'wire wool' is a bundle of strands of very fine soft steel filaments, used in finishing and repairing work to polish wood or metal objects, as well as for household cleaning.

Steel wool is made from low-carbon steel (low enough to be close to plain iron). It is not made by drawing "steel wool wire" through a tapered die, but rather by a process more like broaching where a heavy steel wire is pulled through a toothed die that removes a thin wire shaving.

Steel wool is commonly used by woodworkers and craftsmen working with paint, lacquer and varnish.

Steel wool should not be used on oak, as traces of iron remaining afterwards may react with tannins in the wood to produce blue or black iron stain. Bronze wool or stainless steel wool may be used to avoid this.

When steel wool is heated, it increases in mass due to the burning iron combining with the oxygen.

Often it is used for professional cleaning processes not only on wooden surfaces but also on marble, stone and glass, because it is softer than these materials. For household cleaning use in many countries, including the United States, steel wool is sold as soap-impregnated pads under such trade names as Brillo Pad, Chore Boy, or S.O.S.

Steel wool also serves as an acceptable form of Ne'itzah (scouring) according to Orthodox Jewish laws of Kashrut.

Another use of steel wool is in rodent control. Small holes are plugged with steel wool which if gnawed on by rodents causes sharp pain in the mouth, and if ingested, severe internal damage, leading to death.

Very fine steel wool is sometimes carried for use as tinder in emergency situations; it burns even when wet, and can be ignited by fire, a spark, or by connecting a battery to produce joule heating. See campfire.