The Fourth Conference on Composite Materials: Testing and Design was held 3-4 May 1976 at Valley Forge, Pa. The American Society for Testing and Materials' Committee D30 on High Modulus Fibers and Their Composites sponsored the conference. J. G. Davis, Jr., National Aeronautics and Space Administration-Langley Research Center, served as conference chairman. Most of the papers presented at the eight sessions are included in this volume which complements the first, second, and third conference publications—ASTM STP 460, ASTM STP 497, and ASTM STP 546, Composite Materials: Testing and Design.