Over the past two decades – a period coinciding with publication of Composites Science and Technology – metal matrix composites (MMCs) have been transformed from a topic of scientific and intellectual interest to a material of broad technological and commercial significance. The worldwide MMC markets in 1999 accounted for 2500 metric tons valued at over $100M. Important MMC applications in the ground transportation (auto and rail), thermal management, aerospace, industrial, recreational and infrastructure industries have been enabled by functional properties that include high structural efficiency, excellent wear resistance, and attractive thermal and electrical characteristics. A suite of challenging technical issues has been overcome, including affordable primary and secondary processing, material design and development methodologies, and characterization and control of interfacial properties. This article describes the technological features that characterize the MMC industry. Matrix/reinforcement systems and primary and secondary processes of commercial significance will be broadly described. Several metrics that underscore the growing maturity of the MMC industry will be discussed, including the emergence of a second tier support industry and the growth of standardized materials and methods. MMC applications in the major markets of ground transportation, thermal management, aerospace, industrial, recreational and infrastructure will be described. Successful commercialization strategies will be discussed and insights for achieving expanded MMC applications will be given. A forward look at candidate approaches for the next generation of MMCs will be provided, including projections of new MMC paradigms.