Most scholars recognize Jesus’s self-reference “Son of Man” in the final form of Mark as clearly asserting his identity as the apocalyptic figure from Dan 7 (and possibly 1 Enoch). While this may be true as a conclusion drawn from a reader’s repeated experience and investigation of the text, those who argue for this view often fail to appreciate fully the inherent ambiguity of the phrase and its developing use in the narrative of Mark. Instead of explaining away or ignoring the ambiguity, we ought to seek ways to understand Mark’s use of ambiguity as meaningful. The Jewish apocalyptic worldview of Mark provides such an avenue. Joel Marcus, Elizabeth Shively, and others have argued that the entire Gospel is presented in an apocalyptic light featuring cosmic conflict, eschatological discourse, revelation of heavenly mysteries, and more. The motif of hiddenness and revelation is especially prominent and might be seen in important features of Mark such as the declarations of Jesus’s sonship (baptism, transfiguration, centurion), the secret of the kingdom of God, and the function of parabolic discourse. This paper will argue that in the apocalyptic context of Mark the ambiguity of “Son of Man” purposefully sets up both characters and readers for a moment of revelation. I will trace the development of the phrase through the narrative of Mark. The meaning of the phrase and its application to Jesus are veiled in purposeful ambiguity and misdirection in Jesus’s early public controversies (2:10, 28). However, in private teaching to apostles, Jesus reveals a bit more, associating the phrase with the apocalyptic concepts of suffering and vindication of the faithful (chs.8-10). Finally, the meaning of the phrase is most fully revealed (both to characters and readers) at Jesus’s trial (14:62) where it is tied strongly to Dan 7:13 and unambiguously applied to Jesus himself. Thus, this paper will show that Mark’s use of “Son of Man” is apocalyptic not only in its content but also in its function.