Nondestructive testing (NDT) can be a major part of building preservation and rehabilitation technology. However, before a specific technique can be widely used, it is necessary to quantify its performance envelope by testing it against appropriate standards. Three types of test standards can be used: (1) actual structures, (2) test walls, and (3) computer simulation. The opportunities for tests on actual historic structures are negligible because of the need for confirmatory destructive testing. Testwalls or mockups can be successful if properly designed. Computer simulation holds promise for the future, especially if combined with computer-aided design and drafting (CADD) systems. For reliable simulation, it is necessary to know the fundamental relationships between the NDT signals and the physical phenomena involved.