This chapter explores Marcus’ concept of the soul and its main cognitive parts (hēgemonikon, nous, dianoia, daimon) and their relevance for the construction of a concept of the self that is closely interwoven with Stoic self-care. It also investigates Platonic influence on Marcus’ concept of the mind and its relation with the body. Selfhood, understood as an entity referring to itself, unfolds around the hēgemonikon and, to a lesser extent, the dianoia. Self-reference by cognitive acts is limited to the logical soul. These three rational elements are subordinated to the ‘I’ (or psychagogic subject) and serve as objects of its psychagogic self-(trans)formation, thereby construing its selfhood. The perfect starting point for mental self-transformation in Marcus is hypolēpsis ‘assumption’, a single mental act, similar to Epictetus’ prohairesis ‘choice’, to which Marcus’ concept of mental selfhood is heavily indebted. Platonising rhetoric supports the delineation and detachment of the soul’s rational part (esp. nous) from external entities and subordinate mental phenomena but offers no evidence for a dualist psychology or metaphysical concept of the mind. Instead, Marcus’ concepts of mind and body abide by Stoic orthodoxy and its materialist monism.