Integrating two companies following a takeover or merger has become a highly sophisticated exercise in recent years. Businesses are more disciplined and systematic about identifying and capturing the available synergies. Project tools and techniques are now more subtle and refined.

Yet for all the "scientific" advances, senior executives remain deeply frustrated about their ability to master the art of the takeover. They are less concerned about the familiar and widely documented finding that most mergers fail because acquirers wildly overpay for their targets or ignore the basic rules of integration. What bothers, indeed alarms, an increasing number of thoughtful managers is that integration efforts regarded as beneficial by the standard of synergy targets met (or even exceeded) may justifiably be reckoned as failures from a wider and longer-term perspective. An apparently successful merger can ultimately weaken the combined enterprise—its brand, customer relationships, ability to introduce new products and services, and the morale of its employees—thereby offsetting any short-term financial and operational gains.

Our research, involving a detailed survey of 167 deals and in-depth conversations with nearly 30 CEOs who are veterans of the merger scene, has convinced us that what's often missing is a well-defined, imaginative, energetic, and outward-looking role...