--- - |2 This paper addresses the radical departure of late Bion's and Winnicott's clinical ideas and practices from traditional psychoanalytic work, introducing a revolutionary change in clinical psychoanalysis. The profound significance and implications of their thinking are explored, and in particular Bion's conception of transformation in O and Winnicott's clinical‐technical revision of analytic work, with its emphasis on regression in the treatment of more disturbed patients. The author specifically connects the unknown and unknowable emotional reality‐O with unthinkable breakdown (Winnicott) and catastrophe (Bion). The author suggests that the revolutionary approach introduced by the clinical thinking of late Bion and Winnicott be termed quantum psychoanalysis. She thinks that this approach can coexist with classical psychoanalysis in the same way that classical physics coexists with quantum physics. - The Psychoanalytic Quarterly, Volume 86, Issue 4, Page 753-794, October 2017.