The use of coatings to protect metals against corrosion is well covered by Guides in this series. This Guide breaks new ground by discussing the use of coatings primarily to impart desired physical properties to the surface of a metallic substrate. The physical properties that can be imparted are surface mechanical properties, principally resistance to wear, electrical properties such as high surface conductivity and low contact resistance, and optical properties such as very high or very low reflectance. This Guide concentrates on the first category, viz. coatings resistant to wear including those used to aid the manufacturing process itself; these are loosely called 'engineering coatings'.