"According to the 9/11 Commission, constraining the mobility of terrorists is one of the most effective weapons in fighting terrorism.This report (1) describes key gaps the U.S. government has identified in foreign countries' capacity to prevent terrorist travel overseas, (2) evaluates how U.S. capacity-building efforts address those gaps, and (3) assesses the extent to which the U.S. government is measuring progress in its efforts to close those gaps.To identify the key gaps, GAO reviewed governmentwide assessments of vulnerabilities in the international travel system. GAO reviewed the strategies and documentation of U.S. agencies funding and/or implementing foreign capacity-building efforts to prevent terrorist travel overseas, including those of the Departments of State (State)-which coordinates U.S. efforts overseas-Defense (DOD), Homeland Security (DHS), Justice (DOJ), and the U.S. Agency for International Development (USAID). GAO also interviewed officials from the National Security Staff, of the National Security Council (NSC), which oversees counterterrorism policy. GAO met with these agencies and conducted field work in Kenya, Pakistan, the Philippines, and Thailand. GAO recommends that (1) State develop a mechanism to improve coordination of various agencies' efforts to provide fraudulent travel document training to foreign partners, and (2) NSC develop a mechanism to measure, track, and report on overall progress toward the goal..."