Leading jihadist groups such as al-Qaeda and the Islamic State dominate through cooperation in the form of knowledge sharing, resource sharing, joint training exercises, and operational collaboration. They build alliances and lesser partnerships with other formal and informal terrorist actors to recruit foreign fighters and spread their message worldwide, raising the aggregate threat level for their declared enemies. Whether they consist of friends or foes, whether they are connected locally or online, these networks create a wellspring of support for jihadist organizations that may fluctuate in strength or change in character but never runs dry. Nexus of Global Jihad identifies types of terrorist actors, the nature of their partnerships, and the environments in which they prosper to explain global jihadist terrorism's ongoing success and resilience. Nexus of Global Jihad brings to light an emerging style of "networked cooperation" that works alongside interorganizational terrorist cooperation to establish bonds of varying depth and endurance. Case studies use recently declassified materials to illuminate al-Qaeda's dealings from Iran to the Arabian Peninsula and the informal actors that power the Sharia4 movement.