Tehran’s ability to fight by, with and through third parties in foreign jurisdictions has become a valuable and effective sovereign capability that gives Iran strategic advantage in the region. Tehran has possessed a form of this capability since the Islamic Revolution in 1979, but its potency and significance have risen sharply in the past decade, to the point where it has brought Iran more regional influence and status than either its nuclear or ballistic-missile programmes. The IISS Strategic Dossier Iran’s Networks of Influence provides an understanding of how Iran builds, operates and uses this capability. Based on original field research, open-source information and interviews with a range of sources, the dossier conducts an audit of Iran’s activities in the principal regional theatres of Iraq, Lebanon, Syria and Yemen, and its reach into Bahrain, Saudi Arabia and Kuwait. It includes an examination of Tehran’s nurturing of groups such as the Houthis in Yemen, the Badr Organisation in Iraq, Hizbullah in Lebanon and Shia militias in Syria, and details related to recruitment, weapons supply, logistics and command-and-control systems. Iran’s Networks of Influence is intended through objective, fact-based analysis to inform both policymakers and practitioners, and to stimulate debate on the wider significance of Iran’s use of third-party partners and the strategic depth they afford Tehran. The dossier also examines the advantages that Iran possesses through its recent experience of conflict, and its ability to mobilise and deploy sympathetic Shia communities across theatres. In a time of rising tension in the region, the dossier looks at how Iran might further develop the use of its partnership capability and the risks and constraints it might face.