How are we to explain the fact that we can refer to objects by means of mental acts? And what accounts for our being conscious of mental acts? Rene Descartes and Gottfried Wilhelm Leibniz provide fascinating answers to these two central questions of the philosophy of mind. In this study, the concepts of both authors are analyzed in detail, compared with each other and related to current positions. The analyses show that Descartes represents a deflationary conception of consciousness (conscientia). Consciousness is "only" an aspect of intentionality that constitutes the essential feature of the Cartesian mind. The analyses of Leibniz unveil that he represents a far more complex and demanding conception of the mind in comparison to Descartes, which makes for a higher connectivity with contemporary convictions. The salient features of his position are the structural conception of intentionality and the distinction between two forms of consciousness (apperception and conscientia) that correspond to the phenomenal consciousness and the reflexive self-consciousness. In contrast to Descartes, Leibniz also assigns consciousness to non-rational animals in the form of apperception. Conscientia, on the other hand, is reserved for rational substances.