Language problems top the list of the many obstacles to U.S. investigations abroad, with organizational differences among law enforcement agencies a close second. Limitations in U.S. laws and international laws that differ among countries also create difficulties. Methods available to gather evidence abroad include: (1) police-to-police assistance involving a request through the International Criminal Police Organization (INTERPOL) or through the U.S. agency's representative in the U.S. embassy; (2) mutual assistance through another country's compulsory process, which requires the local prosecutor's active involvement; (3) multilateral treaties or conventions, which bind the countries that ratify them; (4) letters rogatory, where a court requests that a court in another country use its compulsory process to obtain evidence; (5) executive agreements; and (6) extradition, a formal process governed by treaty.