The paper discusses the various modes of wear, the mechanisms involved in each, and the mitigation of wear in some of the modes. The various modes of wear included are: (1) adhesion, (2) abrasion, (3) corrosion, and (4) surface fatigue. Fretting (fretting corrosion or friction oxidation) is a special combination of adhesive, corrosive, and abrasive wear. Adhesive wear is one of the most prevalent types of wear. It can best be explained using the adhesion theory of friction, which is based on contact of surfaces through asperities. Welding occurs at the contacting asperities, and shear takes place at the welds during relative motion. The shear strength at these welds is strongly influenced by contamination, either deliberate or accidental. There is a marked influence of crystal structure on friction and adhesive wear. In general, the hexagonal structure gives lower friction and wear than the cubic structure. Experimental studies show that the lattice parameters in hexagonal crystals also affect friction. Abrasive wear involves damage to soft surfaces by a hard surface, either one of the two surfaces, or a third body. Hardness, work hardening, crystallite orientation, and elastic modulus of the contacting surfaces can all influence wear. Corrosive wear involves corrosion, followed by wear of the corrosion film. Surface fatigue normally appears as local pitting or flaking. Wear damage of this type is a function of the number of stress cycles. All modes of wear lead to loss of dimensional tolerances, high operating costs, and excessive expense (in time and money) for replacement of worn parts. A complete understanding of the basic mechanisms of wear permits alleviation and mitigation.