An important measurement for any new material, for either science or engineering applications, is the determination of the elastic constants. Some exotic new materials, particularly in the crystalline form, may at first be available only in very small samples, and it is challenging to measure such small samples. Recently a new technique, resonant ultrasonic spectroscopy (RUS) has been developed for measuring the elastic constants of very small, as well as large, solid materials. The RUS technique involves lightly contacting a sample with two transducers and using a swept continuous wave excitation to determine a set of resonance frequencies for the sample. A computer calculation is then sued to determine all of the elastic constants from the resonance frequencies. In the past, the technique was hindered by the time required for the computer calculation, but now common desk-top computers can perform the calculation in minutes. For small or large samples, the technique has an advantage in that it is not necessary to bond transducers to the sample; the sample may simply be placed in a holder, and the elastic constants determined in a matter of minutes.