The Harm Principle maintains that the only legitimate reason for limiting a person’s freedom is to prevent that person from harming others. The Posthumous Harm Thesis maintains that it is possible for an act to harm a person even if the act takes place after the person is dead. If this is true, then acts that might otherwise appear to be harmless may in fact prove to harm someone, and acts that might otherwise appear to be consistent with the Harm Principle might turn out to violate it. One must therefore consider whether posthumous harm is possible. This chapter sets out a three-premise argument in defense of the Posthumous Harm Thesis, considers some of the objections that have been raised against them, and examines ways to overcome these objections. Its goal is to show that the argument for the Posthumous Harm Thesis is considerably more robust than is often thought.