Vladimir Putin's full-scale invasion of Ukraine in 2022 has cast a spotlight on Russia's newly sturdy partnership with Iran. Moscow looked to Tehran for drones and ammunition to fuel its so-called 'special military operation', and Iran's support for Russia's war reflects a decade-long strengthening of Russo-Iranian ties, beginning with the 2011 outbreak of the Syrian Civil War. Despite a relationship historically marred by mistrust and unmet expectations, the two regimes have worked together to promote their common interests in Syria, where battlefield coordination soon developed into much deeper political alignment. Drawing on extensive Russian and Persian primary sources, and interviews with elites from both countries, Nicole Grajewski uncovers the drivers of ever-closer cooperation between the Kremlin and the Islamic Republic. Detailing the internal structures, shared anxieties and broader ambitions underpinning this alignment, she explores the genesis of Russia and Iran's mutual antagonism towards the Western-led global order; the impact of deep-seated leadership concerns over regime security and domestic protests; and the future trajectory of the partnership within the larger world order. Examining both military dynamics and economic endeavours, as well as elaborate sanctions evasion schemes and collaboration within international organisations, this is the definitive account of contemporary Russia-Iran relations.