This study uses personally collected data from 41 steel production lines to assess the effects of Japanese and U.S. human resource management (HRM) practices on worker productivity. The Japanese production lines employ a common system of HRM practices including: problem-solving teams, extensive orientation, training throughout employees’ careers, extensive information sharing, rotation across jobs, employment security, and profit sharing. A majority of U.S. plants now have one or two features of this system of HRM practices, but only a minority have a comprehensive system of innovative work practices that parallels the full system of practices found among the Japanese manufacturers. We find that the Japanese lines are significantly more productive than the U.S. lines. However, U.S. manufacturers that have adopted a full system of innovative HRM practices patterned after the Japanese system achieve levels of productivity and quality equal to the performance of the Japanese manufacturers. This study’s evidence helps reconcile conflicting views about the effectiveness of adopting Japanese-style worker involvement schemes in the United States. United States manufacturers that have adopted a definition of employee participation that extends only to problem-solving teams or information sharing do not see large improvements in productivity. However, U.S. manufacturers that adopt a broader definition of participation that mimics the full Japanese HRM system see substantial performance gains.