The United States Supreme Court’s expansion of the Federal Arbitration Act (the “FAA”) has made arbitration clauses ubiquitous in consumer and employment contracts and provoked heated debate. Recently, though, arbitration clauses have become common in a different context: wills and trusts. Courts have reached wildly different conclusions about whether these provisions are enforceable under state arbitration law. However, no judge, scholar, or litigant has considered the more important question of whether the FAA governs these terms. This Article fills that gap. It first examines the statute’s text and legislative history and concludes that Congress intended the FAA only to cover arbitration clauses in “contracts.” Nevertheless, the Article shows that the Court has not rigidly enforced this predicate. As a matter of federal common law, the FAA applies if there is a plausible argument that the parties have agreed to arbitrate—even if the arbitration clause does not appear in a document that meets the black-letter test for contractual validity. The Article then claims that this approach has opened the door for the FAA to govern testamentary arbitration clauses. Indeed, when trustees, executors, and beneficiaries accept fees or property under a will or trust, they also manifest assent to the instrument’s terms. Finally, the Article analyzes how some of the most challenging features of the Court’s interpretation of the FAA—including the scope of the statute, the separability doctrine, and preemption—would play out in the field of wills and trusts. By doing so, the Article seeks not only to provide guidance for courts and policymakers but also to illustrate that testamentary arbitration may not suffer from some of the flaws that make contractual arbitration so polarizing.