For some years now, CEOs have turned to integration managers—usually mid- to upper-level executives relieved of their customary duties for six months to a year—to help lead the task of integrating companies after big mergers or acquisitions. Although an integration manager can contribute significantly to the realization of a merger’s promise, the implementation of this important role often bedevils CEOs, few of whom have sufficient experience with mergers to hit on a plausible formula. No surprise, then, that the effectiveness of integration managers varies widely.

Many CEOs see them simply as process coordinators or project managers. But the best play a far more pivotal role, helping mergers to succeed by keeping everyone focused on the issues that have the greatest potential for creating value and by infusing integration efforts with the necessary momentum. Unfortunately, however, too many integration managers never assume such a role or, if they do, find it hard to succeed in it. Our experience during the past five years with more than 300 integration efforts—most involving Global 500 corporations—suggests three reasons: CEOs fail to recruit the right people for the job; integration managers don’t become involved in the merger process early enough; and CEOs fail to...