Most of the instruments now used for materials research are too complex and expensive for individual investigators to own, operate, and maintain them. Consequently, they have become increasingly consolidated into multi-user, small to midsized research facilities, located at many sites around the country. The proliferation of these facilities, however, has drawn calls for a careful assessment of best principles for their operation. With support from the Department of Energy and the National Science Foundation, the NRC carried out a study to characterize and discuss ways to optimize investments in materials research facility infrastructure with attention to midsize facilities. This report provides an assessment of the nature and importance of mid-sized facilities, their capabilities, challenges they face, current investment, and optimizing their effectiveness.