Composite materials are used in high-performance applications where achieving low weight is of concern. Since their introduction in the early 1960s, composite materials consisting of strong ?bers in a polymer matrix have received considerable success. Because of the great variety of ?ber and matrix combinations, there is no general data base of material properties available for the designer of composite structures. Design of composite materials demands accurate experimental determination of the mechanical properties of the composite materials considered. The emphasis of this article is on the experimental characterization of composite materials in the most basic loading con?gurations, viz. tension, compression, and shear. The description of the test methods is limited to in-plane mechanical response, with the exception of short-beam shear testing.