The number of strategic alliances between large, established firms and small, new ventures is on the rise-especially in industries affected by technological change. Theoretically, the combination of a smaller firm's know-how with a larger firm's marketing system and financial prowess promises synergies that can contribute to both firms' competitive advantage. Yet few of these partnerships result in tangible benefits. On the contrary, strategic alliances often end in disarray, with nothing to show but wasted time and money, and possibly even a lawsuit. The core hypothesis forwarded in this study is that a major cause for cooperative failure is managerial, and therefore controllable and potentially avoidable. Although today's managers are well-trained in competitive behavior, cooperative situations require different skills—skills that a majority of managers do not possess. As a result, cooperation often appears to be managed reactively, rather than being based on a deliberate, proactive cooperation strategy. A thorough analysis of six cases yields a theoretical model that describes the major factors impacting the evolution of strategic alliances. Based on this understanding, three opportunities for managerial influence are investigated: the negotiation process; the boundary-spanning process; and cooperative flexibility. Negotiations must lay a sound foundation for a cooperative relationship, by establishing both a viable cooperation strategy on the basis of complementary resources and compatible interests, and by providing a clear concept for implementation to give the cooperation a “running start.” Conscious boundary-spanning needs to bridge existing organizational incompatibilities, promote the creation and maintenance of trust and goodwill, and deal with conflicts. Finally, partners are subject to the forces of change altering their market positions, resources, and internal situations, which also affect their interests in the alliance. Therefore, success in strategic alliances is closely tied to the ability to be flexible and adjust the cooperation to these changes, including the timely termination of the relationship. The force of using managerial discretion in these areas to shape the evolution of strategic alliances is demonstrated in the description of one case. Although the conclusions and recommendations presented in this article are only based on the investigation of a few cases, the results have been confirmed in other instances observed by this and other authors. At the very least, they may offer a starting point for academic discussion and point the way for a deliberate, proactive cooperation design, replacing a reactive cooperation mode.