Introduction A wealth of information can be derived from instrumented indentation testing (also called nanoindentation); this testing provides the necessary data for the determination of Young’s modulus, hardness, elastic/plastic work, and other material properties. Over the years a set of generalized rules have been empirically determined including the 10% Rule for indentation depth on coatings, the 5% Rule for surface roughness, and the 1 Degree Rule for surface tilt and alignment. This article addresses each of these rules and provides justifi cation and limitations for each.