Memory is a recurring theme in Jean-Paul Sartre's work. However, Sartre never formulated an explicit theory of memory. When he did discuss memory he reached two conflicting conclusions: (1) in his theory of imagination and in his early text The Transcendence of the Ego memory is presented as a mimetic power and memories are repetitions of the past; (2) in his other texts, among them Being and Nothingness, memory is portrayed as a creative force that reconstructs experience rather than repeats it. I argue that Sartre held two conflicting notions of memory since he thought that recollection as a whole—understood either in mimetic or reconstructive terms—stifles consciousness and obstructs freedom. In the dissertation I explore the ways in which memory becomes responsible, according to Sartre, for the constitution of selfhood and for the creation of a solid character with a defined history, which eventually leads to the evasion of the free agency of consciousness. Against the mimetic and reconstructive models of memory I pose the notion of "existential memory", which is not a term that Sartre himself used but which emerges from his work on human temporality. The notion of "existential memory" provides an opportunity to conceive of a possibility of relating to the past in an authentic manner, without objectifying it or losing sight of one's freedom. In response to the challenges raised by Sartre's concerns with bad faith, existential memory is a model of authenticity.