This article examines the legal relationship between terrorism and other transnational crimes. It considers how terrorist groups instrumentally commit other transnational crimes in order to support their terrorist activities, as well as when terrorist acts can qualify as other transnational crimes. The overlap and differentiation between terrorism and transnational organised crime is explored by reference to the UN Transnational Organised Crime Convention 2000 (UNTOC) and its three protocols on human trafficking, migrant smuggling, and firearms trafficking. In particular, the article examines the distinction between politically motivated terrorism and the financial or material benefit that is central to the definition under the UNTOC. Beyond the UNTOC, the article then investigates the relationship between terrorism and a cluster of more disparate transnational crimes, including drug trafficking, illicit trafficking in cultural property, illicit exploitation of natural resources and environmental crimes, and kidnapping for ransom. The article identifies gaps in existing legal regimes.