Strategic alliances are indispensable for accessing specialized resources, capabilities, and know-how that companies cannot easily develop in-house. However, despite being critical for innovation, alliances can be fraught with distrust, particularly regarding concerns about losing intellectual property (IP). A telling case is the failed alliance between American Superconductor Corp. (AMSC) and wind turbine producer Sinovel. AMSC provided essential software for Sinovel's turbines, but Sinovel reverse engineered the software to introduce its new turbines without AMSC. In another recent case, sportscar maker Saleen Automotive accused its joint venture partner of filing 510 patents based on proprietary Saleen technologies and trade secrets worth $800 million, without crediting Saleen's inventors. These cases illustrate how alliances can turn into IP battles, with grave consequences for companies that fall prey to predatory partners. Such battles are more common than may be apparent to external observers, since they rarely receive publicity. Our research reveals that at least 50% of alliances encounter traceable knowledge spillover, and our interviews with executives suggest that this is a key concern in most strategic alliances