It is natural to think that at root, agents are beings that act. Agents do more than this, however – agents omit to act. Sometimes agents do so intentionally. How should we understand intentional omission? Recent accounts of intentional omission have given causation a central theoretical role. The move is well-motivated. If some form of causalism about intentional omission can successfully exploit similarities between action and omission, it might inherit the broad support causalism about intentional action enjoys. In this paper (...) I consider the prospects for causalism about intentional omission. I examine two recent proposals: one Carolina Sartorio (2009) defends, and one Randolph Clarke (2010a) defends. I argue these versions fail, and for a similar reason. Reflection on the function of intention for agency brings this reason to light, and motivates a novel causalism about intentional omission. On the account I go on to defend necessarily, an agent J intentionally omits to A only if an intention of J’s with relevant content (or the intention’s acquisition) causes in J a disposition not to A. Though the causal work done by intentions to omit differs in some cases from the causal work done by intentions to act, it turns out that causalism about intentional behavior (i.e., about action and omission) is viable. (shrink)