The reinforcement of elastomers with short fibers results in composites with a wide variety of properties. The performance and properties are a function of fiber type, fiber content, fiber aspect ratio, fiber orientation, fiber dispersion, fiber-matrix adhesion, processing methods, and properties of the elastomer matrix. A composite with almost any desired property can be obtained by manipulation of these parameters. Of the five fibers studied in this work, glass and carbon are the poorest for increasing mechanical properties. The cellulose, aramid, and nylon fibers all reinforce elastomers to give composites of approximately the same magnitude in properties. Alignment of reinforcing fibers by milling creates a significant anisotropy in the composite properties. The degree of fiber alignment is best for glass, carbon, and cellulose fibers. The uniformity of fiber dispersion is again best for glass, carbon, and cellulose fibers. Aramid and nylon fibers tend to clump together and do not disperse easily. Fiber-to-matrix adhesion is a problem. No evidence of consistently good fiber-matrix adhesion is observed except for the precoated cellulose fibers. The interaction between fiber and elastomer can only improve with a coating or sizing that is compatible with both the fiber and its matrix. Adhesion-promoting bonding agents also improve fiber-matrix adhesion. However, each fiber and/or elastomer may be influenced differently by a bonding agent. Adhesion promoters specific to the type of composite being prepared must be sought in order to obtain optimum properties.