Rapid technological change in recent years has been accompanied by an increase in both traditional and new forms of transnational crime. Particularly serious are international narcotics trafficking, international terrorism, organized crime activities, fraud, and violations of industrial regulations. In individual cases, international cooperation has taken the form of information exchange, informal and formal assistance during investigations, extradition and informal techniques for securing a defendant's presence for trial, and assistance in enforcing criminal judgments. Equally important are efforts to improve general national capabilities for addressing crime such as regular collection and exchange of criminological findings, innovations in law and procedure, and technological developments. To this end, national and international research and crime surveys, along with a wide variety of procedural and technological advances, have made important contributions. Training sessions for multinational participants are the most immediately useful form of international cooperation. Notes and an addendum outlining current and proposed practice concerning extradition in the United States are included.