Epstein is a senior fellow for science and security in the Center for Strategic and International Studies' Homeland Security Program, where he codirects the Global Forum on Biorisks. He is also an adjunct professor with the Security Studies Program at Georgetown University's Edmund A. Walsh School of Foreign Service. His expertise is in improving national and global preparedness to mitigate or respond to biological risks of natural, accidental, or deliberate origin, and in ameliorating tensions between the scientific research and national security communities. From 1996 to 2001, Epstein worked at the White House Office of Science and Technology Policy (OSTP), serving for the last year in a joint appointment as assistant director of OSTP for national security and senior director for science and technology on the National Security Council staff. He previously worked on science, technology, and national security issues at the congressional Office of Technology Assessment, where he directed the office's assessment of proliferation of weapons of mass destruction.