Watch lists provide decisionmakers with information about individuals who are known or suspected terrorists and criminals. Watch lists are important tools used by Federal agencies to help secure the Nation's borders by preventing individuals on a watch list from entering the country, apprehending them after they are in the country, or apprehending them as they attempt to leave the country. This GAO study used a questionnaire to survey nine agencies that perform border security functions and that either develop or use watch lists. The survey found that the Federal Government's approach to using watch lists in performing border security work is decentralized and nonstandard, largely because the watch lists were developed for individual agencies' unique missions. The 9 Federal agencies surveyed have developed and maintain 12 watch lists. These lists include overlapping but not identical datasets, and different policies and procedures govern whether and how these data are shared with others. Generally, sharing of watch list information is more likely to occur among Federal agencies than between Federal agencies and either State and local government agencies or private entities. The extent to which such sharing is achieved electronically is restricted by basic differences in the watch lists' systems structure. This report recommends that the Secretary of the Department of Homeland Security (DHS), in collaboration with the heads of the other departments and agencies that have and use watch lists, lead an effort to consolidate and standardize the Federal Government's watch list structures and policies. DHS and other agencies involved in this study generally agreed with this report's findings and recommendations. 2 tables, 8 figures, and appended survey instrument and comments from the Justice and State Departments