This study responds to a congressional mandate in the FY2021 National Defense Authorization Act, which calls for the National Academies to address the adequacy of strategies to prevent, counter, and respond to WMD terrorism, and identify technical, policy, and resource gaps. The assessments encompass state-sponsored and non-state actors from acquiring or misusing the technologies, materials, and critical expertise needed to carry out WMD attacks, including dual-use technologies, materials, and expertise. The nuclear and chemical threats studies will result in consensus reports and the biological threat assessment will produce workshop proceedings to advise Congress and relevant government agencies.