Interfacial Phenomena in Composite Materials '91 is a collection of papers dealing with the science of composite interfaces, with emphasis on theoretical modeling, test methods, and characterization methods of polymer matrix, metal, or ceramic matrix composites. One paper reviews the micromechanical test methods used in evaluating mechanical properties of fiber-matrix interface. Another paper shows that the critical fiber length cannot always be considered a material constant in the framework of load transfer models based on the shear lag theory. Microwave plasma treatment is a quick technology to change fiber surface structure as the oxidation or the roughening of the fiber increases fiber-matrix adhesion. Another paper evaluates the effect of improved adhesion on mechanical performance under static, dynamic, and impact conditions. It also examines the role of fiber anisotropy on the performance of high performance polyethylene/epoxy composites. By using the Laser Raman Spectroscopy, the investigator can analyze the effects of the fiber surface treatment, the fiber modulus, the curing temperature on the Shear strength, and the fracture mechanics of the interface. The collection can be read profitably by chemists, biochemists, and academicians involved in material compound research.