The Materials Research Science and Engineering Centers (MRSEC) Impact Assessment Committee was convened by the National Research Council in response to an informal request from the National Science Foundation. Charged to examine the impact of the MRSEC program and to provide guidance for the future, the committee included experts from across materials research as well as several from outside the field. The committee developed a general methodology to examine the MRSEC centers and after extensive research and analysis, came to the following conclusions. MRSEC center awards continue to be in great demand. The intense competition within the community for them indicates a strong perceived value. Using more quantitative measures, the committee examined the performance and impact of MRSEC activities over the past decade in the areas of research, facilities, education and outreach, and industrial collaboration and technology transfer. The MRSEC program has had important impacts of the same high standard of quality as those of other multi-investigator or individual-investigator programs. Although the committee was largely unable to attribute observed impacts uniquely to the MRSEC program, MRSECs generally mobilize efforts that would not have occurred otherwise. Because of an observed decline in the effectiveness of the centers, the committee recommended a restructuring the MRSEC program to allow more efficient use and leveraging of resources. The new program should fully invest in centers of excellence as well as in stand-alone teams of researchers to allow tighter focus on key strengths of the program. In its report, the committee outlines one potential vision for how this might be accomplished in a revenue-neutral fashion.