The Optional Practical Training (OPT) program allows students on F-1 visas to work and extend their residence in the U.S. beyond graduation by 12 months. In 2008, students in science, technology, engineering, and mathematics (STEM) fields were granted an additional 17 month extension of the OPT, opening a new channel by which high-skilled immigrants can enter the U.S. labor market. This paper analyzes unpublished OPT administrative data to better understand the use of the OPT STEM extension by students, schools, and firms. It will explore the similarities and differences between firms that hire workers on OPT STEM extensions and firms that hire H1-B visa holders, as well as the nature of partnerships between individual schools and employers. This paper will also model the determinants of the utilization of this visa across schools to better understand why OPT STEM extensions are so highly concentrated at a few academic institutions.