Cybercrime can be perpetrated by offenders anywhere in the world with an Internet connection. The adverse impacts of cybercrime can be experienced outside of the country in which the perpetrator resides. The transnational nature of this crime challenges traditional notions of jurisdiction and requires cooperation of criminal justice agents across the globe (see also the Teaching Module Series on Organized Crime, particularly Module 11 on International Cooperation to Combat Transnational Organized Crime). This cooperation has been observed, for example, in international investigations of online illicit markets (or dark markets), such as Darkode (i.e., a dark market known for selling illicit goods and services, including access to stolen data and malware). Coordinated efforts between law enforcement authorities from 20 countries led to the identification, arrest, and search of members and associates of this site (U.S. Department of Justice, 2015). Despite this and other successful cooperative efforts between countries, barriers to international cooperation against cybercrime still exist today. This Module explores the notions of sovereignty and jurisdiction relating to cybercrime, international cooperation mechanisms, and the challenges to international cooperation.