No matter how compelling the business case, acquisitions inevitably run into difficulties. Key people leave, processes break down, information systems get tangled, and customers grouse. Most company leaders are blindsided by these impediments—they've focused so hard on nailing down the terms of their deals and hashing out broad integration plans that they've given short shrift to spotting specific problems. The most successful acquirers, however, don't ignore any of the details. Whether problems are manageable or cataclysmic, these acquirers have strong early-warning systems in place to identify them, and they respond to even the faintest distress signals without delay. Their approach can provide a valuable model for any company considering—or surviving—a merger.