We study the relationship between workforce composition and firm productivity based on a new employee-employer-matched data set, using an array of workforce characteristics and three alternative measures of firm productivity. While firm age is not essential for the performance of firms, those of smaller size and those in the steel and transportation industries outperform others. Moreover, labor quality, particularly the middle-aged with higher education, contributes significantly to firms' productivity. Furthermore, economic incentives and market competition both play important roles in the performance of firms. Finally, there is an employer-size premium with larger firms paying higher wages and nonwage benefits. (JEL C33, D20, J30).