In 1980, Robert Spitzer and the DSM-III Task Force initiated a paradigm shift in psychiatric classification, effectively shoring up psychiatry's legitimacy during a period of professional crisis. Thirty years after DSM-III, psychiatry once again finds itself in a precarious position, and once again, the DSM-5 Task Force is attempting to resolve its professional crisis by revising the DSM. However, the very success of DSM-III—both its integration into all facets of mental health and its centrality to psychiatry's professional identity and authority—has made it impossible for the DSM-5 Task Force to duplicate Spitzer's feat. As the DSM-5 revision process unfolds, it has become evident that vehement resistance within the profession has derailed the Task Force's initial dream of introducing significant innovations and even realizing a paradigm shift through dimensional measurement. In recounting how and why the dimensional revisions were defeated, this chapter suggests the limitations of shoring up professional authority through a nosology. The vicissitudes of the DSM-5 process can only be understood by situating it within the professional politics of American psychiatry over the last three decades—a history dominated by the DSM.