Immigration policy is one of the most contentious public policy issues in the United States today.  High-skilled immigrants represent an increasing share of the U.S. workforce, particularly in science and engineering fields. These immigrants affect economic growth, patterns of trade, education choices, and the earnings of workers with different types of skills. The chapters in this volume go beyond the traditional question of how the inflow of foreign workers affects native employment and earnings to explore effects on innovation and productivity, wage inequality across skill groups, the behavior of multinational firms, firm-level dynamics of entry and exit, and the nature of comparative advantage across countries.