This paper argues that the conception of the self as constituted by its act of awareness of itself emerges from the confluence of three medieval ideas: Augustine's concept of endogenous attention, Avicenna's concept of primitive self-awareness, and Olivi's concept of reflexivity as a necessary feature of personhood. It is Descartes who by his rejection of a distinction between a substance and its principal attribute and his weaving together of these three strands of thought who creates a conception of the self which still plays a central role in contemporary discussions.