The Stoic theory of movement has never been the object of a deep investigation despite the considerable number of sources in Neoplatonist commentators. This paper explores for the first time the Stoic notion of ἐνέργεια, which plays a fundamental role in the Stoic conception of movement and generally in the characterization of interaction between bodies. I will show that the Stoics identified movement and activity, so that everything that is active is necessarily moved. This implies that the Stoics merely characterized (...) ἐνέργεια in a dynamic or kinetic sense, namely by connecting it with movement. In order to prove the coherence of this philosophical position to the Stoic doctrine, I will display the compatibility of Neoplatonists’ reports with other sources. Accordingly, I will claim that the Stoics conceived this peculiar sense of ἐνέργεια in reaction to Aristotle, who clearly distinguished between ἐνέργεια and κίνησις in his physical theory. (shrink)