Much research in strategic entrepreneurship has focused on the consequences of network structure for firm performance. Despite this emphasis, little is known about variation in network structure across industries, or about the antecedents of this variation. In a comparative study of alliance networks in 32 industries, we demonstrate substantial variety in network structure, and develop a typology of network structures. We then endeavor to explain this variation by focusing on dimensions of the products and technologies that characterize these industries—such as technological uncertainty and dynamism, product modularity, and architectural control—and associating them with underlying characteristics of network structure. We conclude with a discussion of implications of our findings for research in strategic entrepreneurship. Copyright © 2008 Strategic Management Society.