Plotinus’ views on concepts have so far received little attention, whereas his views on ennoiai, conceptions, have been more widely discussed. This is partly due to the varied vocabulary that Plotinus uses to refer to what we might call concepts, assuming that the latter are understood as mental items distinct from thoughts. Sara Magrin’s chapter ‘Plotinus on Concepts’ focuses on one important passage of the Enneads (Ennead 6.6.12–14) which offers a critical discussion of an account of the concepts (ennoēmata) of one and numbers commonly attributed to the Stoics. The chapter pursues the twofold aim of reconstructing the account in question and of interpreting and assessing Plotinus’ criticism of it. This has scarcely, if ever, been attempted in the scholarship, both because the evidential value of that passage in respect of the Stoics has been deemed questionable and because Plotinus’ criticism of the Stoic concept of number is extremely compact and difficult to articulate. The main contribution of Magrin’s analysis consists in her use of Plotinus’ criticism of the Stoics as evidence, on the basis of which she pieces together Plotinus’ views on concepts.