Finance may be the most powerful weapon of war. It moves armadas, armies, and squadrons. It funds troops and artillery. It endows suicide bombs and improvised explosive devices. It pays for special forces and mercenaries. It underwrites cease-fires and purchases surrenders. Finance is the weapon that makes all other weapons of war possible. ... This Article is about the financial weapons of war, their growing importance in national affairs, and their wide-ranging effects on law, finance, and society. This Article offers an early, broad examination of the realities of modern financial warfare. This Article descriptively and normatively explores the new financial theater of war, analyzes the modern arsenal of financial weapons, highlights emerging legal and policy concerns, and proposes key recommendations for current and future financial warfare. ... While policymakers, analysts, and scholars have long been studying the respective, evolving fields of modern finance and modern warfare, there has been surprisingly little meaningful legal scholarship on the crosscutting realities of modern financial warfare. Drawing on a rich legal literature that spans the laws of war, finance, and cyberspace, this Article seeks to fill this understudied, underappreciated—yet critically important—legal intersection of war and finance. ... Part I provides a general layout of the modern financial theater of war. It describes the modern financial infrastructure as a globalized, high-tech, American-centric system. ... Part II highlights particular armaments of financial warfare. Rather than provide an exhaustive catalog of financial weapons, it offers a broad inventory of the financial weapons of war. It classifies the financial weapons of war as analog weapons and cyber weapons. ... Part III contends with new concerns. It asserts that the financial weapons of war present critical challenges for traditional laws and norms relating to financial hostilities, cyberattacks, and non-state actors. ... Part IV offers new pathways. It proposes three pragmatic policy recommendations that should be undertaken in the near term response to modern financial warfare while larger issues remain unresolved by global policymakers.