This paper examines an important but neglected topic in Suárez’s metaphysics–—namely, his theory of efficient causation. According to Suárez, efficient causation is to be identified with action, one of Aristotle’s ten highest genera or categories. The paper shows how Suárez’s identification of efficient causation with action helps to shed light on his views about the precise nature of efficient causation, and its role in his ontology. More specifically, it shows that Suárez understands efficient causation to be a distinctive or sui (...) generis type of entity, and that he thinks we must adopt this view in order to account for the facts of efficient causation. The paper also examines several objections to Suárez’s account. (shrink)