According to the Department of Homeland Security (DHS), “The Global Nuclear Detection Architecture [GNDA] is a framework for detecting (through technical and non-technical means), analyzing, and reporting on nuclear and other radioactive materials that are out of regulatory control.” The Domestic Nuclear Detection Office within DHS asked the National Academies for advice on developing quantitative approaches for assessing the effectiveness of the GNDA and stated that it intended to use this advice to improve the GNDA’s strategic plan.