How is the term “mysticism” used today? Does this term remain scientifically or philosophically significant? Michel de Certeau’s works on the mysticism （la mystique） are provocative attempts to confront this problem. In this paper I recapitulate Certeau’s concept of mysticism, by examining (in chronological order) his important texts on the subject. Though his manner of writing and methodological procedures became progressively more sophisticated and his analyses of the historical contexts of both past mystics and contemporary scholars developed over time, I believe that his understanding of the nature of mysticism remained essentially the same from his earliest treatise to his last. For Certeau, mysticism is the “impossible investigations” of individuals who are seized by a desire to situate the ineffable encounter with the Infinite (what Christians may call God) in the historical reality of this world, through language, action and interaction. However, Certeau maintains that mystical endeavours are always doomed to fail, as the Infinite can never be completely situated in this world. Thus, driven by a desire to fill the void created by the absence of the ineffable, mystics cannot avoid going beyond conventional representations (theories, practices, institutions, experiences, etc.) of the Infinite in order to find more adequate means of expression. This conceptualization of mysticism that does not emphasize the moment of presence of the Infinite in mystical experiences but rather stresses a profound sense of its absence, provides new ways in which to interpretate the writings and actions of mystics, and new ways in which to further consider the nature of the Infinite itself.