Information flows, and thus information technology (IT) are central to the structure of firms and markets. Using data from the U.S. Census Bureau, we provide firm-level evidence that increases in IT intensity are associated with increases in firm size and concentration in both employment and sales. Results from instrumental variables and long-difference models suggest that the effect is likely causal. The effect of IT on size is more pronounced for sales than employment, which leads to a decline in the labor share, consistent with the “scale without mass” theory of digitization. Furthermore, we find that IT provides greater benefits to larger firms by increasing their capability to replicate their operations across establishments, markets, and industries. Our findings provide empirical evidence suggesting that the substantial rise in IT investment is one of the main driving forces for the increase in firm size, decline of labor share, the growth of superstar firms, and increased market concentration in recent years.