High-technology workers of the late twentieth and early twenty-first centuries obviously employ networks to build innovative firms and transform industries. A century and a half before the modern information technology revolution, however, machinists in the eastern United States created the nation’s first high technology industries. In metalworking industries such as iron foundries and steam engine works, locomotive works, general machine shops, textile machinery firms, firearms manufacturers, and machine tools, these resourceful workers pioneered the practice of dispersing technological expertise through communities of practice. In the first book to study this phenomenon since the 1916 classic, English and American Tool Builders , David R. Meyer freshly examines the development of skilled-labor exchange systems, showing how individual metalworking sectors grew and moved outward. He argues that the networked behavior of machinists within and across industries helps explain the rapid transformation of metalworking industries during the antebellum period, building a foundation for the sophisticated, mass production/consumer industries that figured so prominently in the later U.S. economy.