Over the past twenty years, merger control has made what appear to be substantial advances in concepts and methodology, claiming the mantle of a “revolution.” This essay observes, however, that over this very same time period, merger control has in fact weakened and concentration risen throughout the economy. It reexamines two of the most heralded new methodologies—market definition and unilateral effects. It shows ways in which these have had the paradoxical effect of actually weakening merger control rather than strengthening it.