"Diplomatic assurances" are promises not to torture. The US and other traditionally rights-respecting governments have sought these assurances when sending detainees, usually terrorism suspects, to foreign authorities known for torture. This report, the culmination of several years of research by the Human Rights Institute, presents the evolving evidence and jurisprudence of assurances. Without taking a position on whether assurances can work, it describes elements that are necessary to make assurances plausible: judicial review, public scrutiny, and systematic monitoring.