Whether investigating transnational criminal conduct or engaging in the civil discovery process in atransnational proceeding, those involved will almost always be required to collect evidence in foreign countries. National sovereignty, international treaties, and international law, however, preclude U.S. law enforcement officials from simply flying to a foreign country to conduct searches, question suspects, obtain documents, or proceed with arresting individuals for trial in the United States. In the absence of a foreign country’s agreement to cooperate in a criminal investigation or civil litigation, U.S. prosecutors or civil litigation counsel, in short, have limited options. For this reason, transnational cooperation and collaboration are integral, and increasingly important and mainstream, components of contemporary justice systems.

Federal Judicial Center International Litigation Guide