Nuclear forensics is the examination and evaluation of discovered or seized nuclear materials and devices or, in cases of nuclear explosions or radiological dispersals, of detonation signals and post-detonation debris. Nuclear forensic evidence helps law enforcement and intelligence agencies work toward preventing, mitigating, and attributing a nuclear or radiological incident. This report, requested by the Department of Homeland Security, the National Nuclear Security Administration, and the Department of Defense, makes recommendations on how to sustain and improve U.S. nuclear forensics capabilities.