In this article I attempt to demonstrate the relevance of the philosophy of time to psychiatric, psychological and psychoanalytic theories of development and therapeutic action. I choose to explore and analyse the writings of Martin Heidegger, arguably the twentieth century’s pre-eminent philosopher of time. I then develop links between his philosophy and Freudian theories of time, and in particular Freud’s notion of Nachträglichkeit, as advanced in the writings of André Green and Jacques Derrida. I conclude by advancing a range of temporal concepts that may be employed in the analysis of developmental theories and clinical approaches. In an accompanying article I undertake such an analysis, relating in particular to borderline conditions.