In ‘The Stoics on Conceptions and Concepts’, Katerina Ierodiakonou offers an account of the Stoics’ distinction between ennoiai and ennoēmata (‘conceptions’ and ‘concepts’), and also of the distinctions suggested by the standard Stoic terminology of concepts also mentioned above: notably, prolēpseis (‘preconceptions’), phusikai ennoiai (‘natural conceptions’), and koinai ennoiai (‘common conceptions’). All these terms appear intended to point to general notions that play a central role in the acquisition of human knowledge, but it remains puzzling how exactly the Stoics understood them or why they introduced them into their doctrine in the first place. Ierodiakonou addresses these issues, as well as further questions debated in the secondary literature. These include whether all human beings necessarily possess concepts or just have the ability to possess them, what is the content of conceptions and how it is determined, what is the ontological status of conceptions and concepts, and what are their epistemological functions.