The relationship between Iran and al-Qa`ida goes back at least a quarter of a century, but it remains one of the most understudied and poorly understood chapters in the history and evolution of the jihadi organization founded by Usama bin Ladin. Recently declassified letters seized in 2011 from bin Ladin’s Abbottabad hideout and U.S. government and court documents, however, have shed some additional light on their partnership. The existing information suggests that the relationship is best understood as a “tactical cooperation”—one that, despite the intervention of Iran and its proxies in opposition to al-Qa`ida in the Syrian civil war, is likely to continue for as long as the parties perceive the benefits of cooperation to exceed the costs.
Moghadam, Assaf. 2017. "Marriage of Convenience: The Evolution of Iran and al-Qa'ida's Tactical Cooperation." CTC Sentinel 10 (April): 12-18. https://www.ctc.usma.edu/posts/marriage-of-convenience-the-evolution-of-iran-and-al-qaidas-tactical-cooperation