Ultrasonic testing methods that are well established for application to metals and alloys can not be identically applied to composite materials. Because composites are both heterogeneous and anisotropic, complications arise in the mechanics of the interaction of the stress waves with the material. This leads to a variety of new R&D problems that are both difficult and interesting. Attempts to characterize material strength, material (tensor) stiffness, and defect distributions are currently being conducted.