Building on his groundbreaking research first cited in Business Week, Mark L. Sirower explains how companies often pay too much—and predictably never realize the promises of increased performance and competitiveness—in their quest to acquire other companies. Armed with extensive evidence, Sirower destroys the popular notion that the acquisition premium represents potential value. He provides the first formal and functional definition for synergy -- the specific increases in performance beyond those already expected for companies to achieve independently. Sirower's refreshing nuts-and-bolts analysis of the fundamentals behind acquisition performance cuts sharply through the existing folklore surrounding failed acquisitions, such as lack of "strategic fit" or corporate culture problems, and gives managers the tools to avoid predictable losses in acquisition decisions.