Book excerpt: Traditionally the vast majority of materials characterization techniques have been destructive, e. g. , chemical compositional analysis, metallographic determination of microstructure, tensile test measurement of mechanical properties, etc. Also, traditionally, nondestructive techniques have been used almost exclusively for the detection of macroscopic defects, mostly cracks, in structures and devices which have already been constructed and have already been in service for an extended period of time. Following these conventional nondestructive tests, it has been common practice to use somewhat arbitrary accept-reject criteria to decide whether or not the structure or device should be removed from service. The present unfavorable status of a large segment of industry, coupled with the desire to keep structures in service well past their original design life, dramatically show that our traditional approaches must be drastically modified if we are to be able to meet future needs. The role of nondestructive characterization of materials is changing and will continue to change dramatically. It has become increasingly evident that it is both practical and cost effective to expand the role of nondestructive evaluation to include all aspects of materials' production and application and to introduce it much earlier in the manufacturing cycle. In fact, the recovery of a large portion of industry from severe economic problems is dependent, in part, on the successful implementation of this expanded role.