This chapter studies the place of dialectic within Stoicism, where it is understood as a part of logic and a subpart of philosophy. By drawing on comments by Alexander of Aphrodisias, the chapter contrasts the Stoic conception of dialectic to those of Plato and, particularly, Aristotle. It is argued that what makes dialectic a part of logic, and hence a subpart of philosophy, in opposition to the Aristotelian view, is not its utility but its subject-matter, a particular domain of reality, and its purpose, a concern with truth. In support of this, the Stoic position on mathematics, which was not a part of philosophy, and on rhetoric, which was a part of philosophy side by side with dialectic, is considered.