The 2010 National Drug Threat Assessment stated that the availability of illicit drugs is increasing. The Drug Enforcement Administration (DEA), in the Department of Justice (DOJ), works with Immigration and Customs Enforcement (ICE), within the Department of Homeland Security (DHS), to carry out drug enforcement efforts. DEA and ICE signed a 2009 Interagency Agreement (Agreement) that outlined the mechanisms to provide ICE with authority to investigate violations of controlled substances laws (i.e., cross-designation). The Agreement also required DEA and ICE to deconflict (e.g., coordinate to ensure officer safety and prevent duplicative work) counternarcotics investigations, among other things. GAO was asked to assess the Agreement's implementation. This report addresses the extent to which DEA and ICE have taken actions (1) to implement the Agreement's cross-designation, deconfliction, and information-sharing provisions and (2) to monitor implementation of the Agreement and make needed adjustments. GAO analyzed documents such as the 2009 Agreement, related interagency agreements, and directives to field offices. GAO also interviewed DEA and ICE Headquarters officials as well as management officials and first line supervisors in 8 of the 21 DEA and 8 of 26 ICE field offices, based on geographic dispersion. Though not generalizable to all DEA and ICE offices, the interviews provided...