Few practitioners or researchers in psychology would think of the 17th-century French philosopher, René Descartes, as the founding father of their discipline. Yet, it is difficult to see how psychology could have emerged as a discipline in its own right without the contributions of Descartes. Descartes’ theoretical and experimental contributions to our understanding of rationality, consciousness, sensation, feeling, attention, psychological self-regulation and voluntary action, and indeed the very concept of mind that lies at the heart of his philosophy, have been pivotal to the evolution of psychology since its emergence as a special science in the 19th-century. These contributions tend to get overshadowed by the unpalatable aspects of his dualism of mind and body and his denial of animal consciousness, doctrines for which he was and still is much pilloried. However, both doctrines are relevant to understanding how from its inception the subject matter and scope of psychological investigation was framed, for underlying the Cartesian concept of mind is not one dualism but two: a dualism of mind and body and a dualism of life and mind. The mind, for Descartes, could not be theorized on its own terms without conceiving of it at least to some extent independently of the physiological processes of the human body, on the one hand, and the life functions of biological organisms, on the other. Descartes’ legacy for psychology as a discipline is thus twofold. It created the conceptual space for the concept of mind to emerge as a threshold concept in its own right, distinct from the concept of matter that defined mechanics, and it demarcated those uniquely human capacities that enabled psychology to differentiate itself from the newly emerging evolutionary biology of the 19th-century, even though it would remain more closely aligned with biology than physics thenceforth. Without both dualisms of mind and body and life and mind, it is difficult to envisage how psychology as a special science distinct from anatomy and the life sciences could have emerged, and for this the discipline of psychology owes Monsieur Descartes a considerable debt.