Military use of advanced polymer matrix composites (PMC)a consisting of a resin matrix reinforced by high-performance carbon or organic fibersa while extensive, accounts for less that 10 percent of the domestic market. Nevertheless, advanced composites are expected to play an even greater role in future military systems, and DOD will continue to require access to reliable sources of affordable, high-performance fibers including commercial materials and manufacturing processes. As a result of these forecasts, DOD requested the NRC to assess the challenges and opportunities associated with advanced PMCs with emphasis on high-performance fibers. This report provides an assessment of fiber technology and industries, a discussion of R&D opportunities for DOD, and recommendations about accelerating technology transition, reducing costs, and improving understanding of design methodology and promising technologies.